Disclaimer : I live in Yurp and don't know the US market. What's legal on my side of the ocean : 250 W max, assist up to a speed of 16 mph.
For a 3.3 miles trip, unless you're facing a steep gradient, you don't need an electric. (An electric won't help you for a very steep hill, BTW. The extra weight will "over power" the engine.)
That said, you'll get what you'll pay for. A cheap chinese won't hold up well to daily abuse.
What you want is Li Io batteries, or NiM. Forget lead. And a panasonic brushless engine. Battery capacity is not a big issue considering your mileage. You'll need at least 10A/h though.
If your goal is to stay dry, rather than help you bike that extra mile, the dutches makes some very fine bikes. Batavus or Sparta
are the bee knees (they are basically the same bikes). Super reliable, great comfort and adequate performance. But the batteries are integrated to the frame : You can't remove them to plug them at home, you need to plug the bike. Gazelle
(yes, they're chinese) have some alternatives with removable batteries. I'm not found of Giant's FWD engine, but if you don't mind it, they're great value for money.
agattu, a german brand, has a great reputation in the UK and in its home market, but it's not imported where I live. The specs are really interesting and the price seems very reasonable.Flyer
, a swiss brand, makes great and very expensive bikes, more aimed at "real" bikers, ie who want to be assisted rather than powered. It's a very different feel, that may not suits your needs. But the quality is top notch.
The BionX kit is great, but it's a kit : It doesn't have the sleek integrated look of the other options but it's cheaper and works very fine. You'll need a good bike though. Most cheap bikes don't like a daily use, and the electric motor put some extra strain on the bike.
To summarize, IMO, for a short commute in a suit, trust the dutches or the germans. That's what they do, every day. Their bikes are designed for this : Gear hub, fat tyres, drum brakes, integrated dynamo, enclosed chain... They're heavy but they'll last.
You may also want to test that commute a few time before spending some big bucks...
Ps : Demo, demo, demo