Ascension (Black Diamond) skins are discounted very little so therefore you'll seldom find them "on sale" by much more than about 30-40% off retail. I've used a few kinds of skins over the years and the new Ascensions with Clip-Fix are by far the easiest/quickest/best I've ever used. Personally, I'll pay the extra $75-100 for that convenience. Skins last a long time and if you use them a lot, you'll appreciate the ease of use.
Alpine Trekkers work well for what they accomplish and there really shouldn't be much of a safety concern. The problems associated with them have to do with the height of the boot off the ski and the fact that you're (usually) skinning uphill in your alpine boots. For short skinning durations and near-resort OB skiing, they aren't horrible. That's about the best you can say. They lower the cost of getting into backcountry skiing and will help you decide whether you like hiking for your turns without making a huge investment you might later regret. Most skiers find, however, that as they start doing a lot of skinning the Trekkers start to suck more and more.
Packs are very, very personal. It depends on whether you're doing close-in skiing to resorts or whether you're a long way from safety. How much junk you carry in your pack depends on your local weather conditions and how long you're typically away. What's the *worst* that could happen to you on a "normal" day and will your pack carry what you need to deal with it? Do you like to carry skis A-frame, diagonal, or straight up and down (believe me, if you do very much of this, there will be times you'll be carrying your skis). Some packs (like mine, a Vortex 1800) do all three. Will you have more than one pack for different types of outings? Will you ever hike in hiking boots and carry your boots in your pack? Is your pack comfortable and well-suspended even if you overload it? How does it feel on your back when you're skiiing down crappy snow with as much gear as the pack will carry? It should ride close to your back and not swing a lot while you're skiing down.
Dakine probably sells more BC packs than everyone else put together. Here are some others that I or friends really like:http://www.bdel.com/gear/frenzy.phphttp://www.ospreypacks.com/switch_18.htm
(My wife got one of these this past winter and I think it's an incredibly good pack if you're *primarily* a lift-access backcountry skier.)http://www.vortexbackpacks.com/productdetail.php
(This is the modern version of my pack, which I've had for eight years now. Mine is pretty beaten up from an awful lot of use but it still works perfectly.)