This takes me back...
A few years ago, I wanted the same thing you do- race timing on the cheap. What I found is that if any real accuracy is desired, you need to spend a little money and get the real stuff. If people paid to race, they expect accuracy in timing. That's what this sport boils down to. In my intramural league (NASTAR-esque), it's not uncommon to have racers with identical times down to the 1/100 of a second. Can you eyeball a finish that accurately? Spend a little money.
I started out with an old Reliable Racing 2s timer, Reliable Racing start gate, and a TAG Heuer 2-9 photosensor. This was great if you wanted to manually record times and didn't mind fixing the photosensor every year (it required timer power), but it did the job.
There are more than a few of the 2s timers floating around that race teams are probably willing to part with cheaply, and they're fairly bulletproof and easy to fix (I have the schematics). They don't interface with any existing computer software, so you will be recording times manually. I used an Excel spreadsheet, which added the times automatically and did all of the sorting functions. The timer will also power external sensors, which is nice if you're using dinosaur equipment.
From there, you might be able to find an old, non-homologated (approved by FIS) timer, like the TAG Heuer CP501 or CP502. I picked up a couple 502s off of eBay last spring for $250 (for the pair) for a mighty mite program, but I haven't seen many auctions like that. Be careful, as support for these timers is often not available and if they break you either fix them yourself or you're out of luck. The ones I got needed several components replaced before they'd work, and TAG wouldn't provide me with schematics or any other info. Alge is a little better with support, but don't count on any timer manufacturer for help- they want you to buy the new stuff.
A step up from that is an Alge Comet, which will interface with several timing programs and might still be homologated. I think Alge still actively supports this handheld (but still pretty powerful) timer, and it works well in somewhat nasty conditions (battery powered and well-sealed). I expect suport to drop off in a couple years, but they are a good unit for the money (around $500-ish).
A step laterally from that are the Summit Systems SRT500s that reliable racing sells for around $500. http://www.reliableracing.com/detail...&category=6501
I haven't worked with them specifically, and software support is somewhat limited, but some people have reported good results. I usually only deal with TAG Heuer and Alge, since there have been more than a few companies go under that sold timing equipment and left their customers high and dry with expensive door stops. But I would imagine Reliable Racing will give some sort of support in the long term if something did happen.
I have an Alge Timy, which goes for about $1400 (and up). While by no means top of the line for race timers, it's the most versatile I could find and does everything I could possibly need a race timer to do. Amazing how I got from "I don't want to spend any money" to this point.
After the timer, you need a good start gate. I looked at building them, but it got expensive pretty darn quick. The switch alone was about $150 for the accuarcy and reliability/durability you need. You might find a race team with an automatically returning gate that they will let go cheap. I still use my Reliable Racing gate as a backup, and it works perfectly- it's just not homolgated. Expect to pay about $600 if you can't find one on the used market.
For finish sensors, you can get an old Alge RLS1 (refurbished) for under $400 from Phoenix Sports Technology http://www.phoenix-sports.com/
which would be pretty durable and suit your purposes. Used TAG and Alge sensors show up once in a great while on eBay, but usually in the late spring and not always at the best prices. Used stuff sometimes shows up on the Phoenix Sports Technology bulletin board, and I would consider that a better source for equipment. As for using photosensors designed for other applications, you may have issues with fogging or other failures related to the conditions usually found at ski resorts. I never had much luck with them, but your results may vary.
For the rest of it, you can go pretty cheap. PC Timing software is available for free for several common timers (I use Skunkware's Fiddleware program). Wiring from the start gate can be normal CAT 5 cable, or something else in the 24 gauge or larger size. You really only need a single pair for starts, but more pairs is better for reliability. Don't expect to be able to remove the wiring once it's on the ground unless you used wire specifically designed for cold weather (much more expensive)- it will break. For the finish sensor, you should use a better grade of cable, especially if you're running power through it to the sensor. Fortunately, in a standard configuration you will only need a short run from the finish to the timer.
Wireless systems are another option (like the ones from Brower), but reliability can be an issue and they can get kinda spendy. I tried to modify their handheld wireless track timer for ski racing (another eBay find), but results were less than ideal. Radio interference was the biggest issue once I sorted out the other problems, and I ended up selling the thing a year later. I just couldn't rely on it.
For a person who wanted to do timing on the cheap, I have spent over $5,000 on my current system. I like Alge's stuff because it's the most durable I've found, has good support, and it's easy to work on. I ended up with a Timy, RLS1-n photosensor, D-Line display, TED wireless transmitter/receiver, and an old TAG start gate. When you add in the gates and other equipment required to run a race program, it's well over $10,000 (and climbing).
I could have done it cheaper, but reliability on race night is of paramount importance to me. There's nothing worse than spending hours setting up a course and timing, having racers at the start, and having to postpone the race because of equipment failure. I know, it's happened to me in the past.
But, I don't see why you couldn't put a system together for much cheaper. Start with a used Reliable Racing 2s timer ($50?). Add a refurbished Alge RLS1 ($350?) for the finish sensor. Finding a start wand might be difficult, but let's say $150. That would give you a basic system for around $650 that can handle multiple racers on course at one time and will be accurate to 1/100 of a second.
If you have any questions, let me know. I should be able to point you in the right direction for what you're trying to accomplish.