In addition to all that was said above, I'll add to take the wattage claims of those "kit" panels with some skepticism. My 45W Harbor Freight Kit has
never gotten anywhere near 45W. Best I ever got - fresh out of the box, carefully aimed at the July noonday sun - was 30W and I more routinely get 20-25W since.
Besides, it takes quite a bit more space to fit the same wattage with amorphous panels.
Over the past few months I have installed several Kyocera 135W panels on the roof, and I consistently see only slightly below STC and well above PTC ratings. (STC is the "ideal" test you really aren't ever going to get. PTC is the "real world" test rating that you should realistically be able to get.) That's without any careful aiming, just flat to the roof.
You get what you pay for!
Have you tried the actual solar stores? I have never been very trusting of anyone dealing through Amazon or (especially) E-Bay. But then I'm a big-time cynic and don't trust much of anyone...!
I did a quick run through the store I bought my new panels from - Northern Arizona Wind & Sun - and came up with these items:
http://store.solar-electric.com/kykc50wasopa.html
50W Kyocera multicrystalline panel - $279
http://store.solar-electric.com/ss-6.html
SunSaver 6 amp charge controller - $44
Pretty close to your $300 limit, although you will have to provide some wiring. Might be able to run two of those panels on the charge controller, if desired - it's pushing the limits if you use the STC ("ideal") ratings, PTC shows 2.5A max. (You can get manufacturer data sheets on their site too, which will have the specs and output charts.) All in a panel just 2 foot square, instead of four separate ones!