$500 is going to get you a nice little package. Get the basic box locally due to it's size and weight being too expensive to ship. For a amp, I have many suggestions for you, start with the Infinity Reference 7541A 4 channel amp and bridge it to run two 12" or 10" subs. Down the road this amp can be used to power the front speakers and a larger mono amp used on the subs. Pioneer has some nice 12" subs in the Premiere line that have a great 2 year warranty on them. As far as pricing goes, the Infinity amp is normally quite expensive, up around the $450 mark IIRC. RIght now I have two left for $230.00 each, new, with warranty. This is a far better match of your $ to equipment than 1,2,4 or more of those FS packages.

 

In this case I would say go with quality over quantity. As recommended above, you are better off to investigate better built, higher output products. Once you start with car audio, you will keep going. Better off to start with a decent product that you will be able to use later on in a different setup (corresponding to what mr2nr said.)

 

buddy of mine bought an infinity amp off of MR2NR and it is awesome and you can get L7's of of ebay around 1-200 so ya i would go that way

 

Check out the Fusion Bass Packs.
In your $500 Budget you should be able to get the Powerplant 12" sub and amp.
The amp puts out over 500 RMS, and it comes with a decent ported box, and an amp install wiring kit.