I agree from what I've read, that it's best to go for as high a wattage panel as possible, and the highest quality, seeing this is THE key element to your solar system. If you can't collect it, you can't use it!
Also, remember you don't have to use that extra power you might happen to collect, so the more panels the better. But the big cost is batteries, seeing they will last, generally, about 3-5 years, and decent ones can cost several hundred dollars each.
Car alternators? These can be had for cheap, and many can be rebuilt to like-new condition for even less, but go for the most amps(commercial vehicle types) you can get because it doesn't matter how the alternator turns, just so long as it turns as fast as possible, and long as possible.(Got a bunch of hamsters just sitting arond?)