You seem to be falling into the cheap boat quickly to put it blunt. If you need to go cheap. Buy one thing at a time and save for the parts and upgrade as money comes around. The bad thing is to redo something twice. I know I have had my car apart over 16 times trying different speakers, amps, and head units.
Sense you already bought the sony that is already there. Unless you did not look at the lower end kenwoods they are great band for the buck and offer a lot.
For a amp here are a few well priced amps. Not all amps can run a sub and speakers well.
5350a - Infinity 5 Channel Amplifier
PA500.4 - Polk Audio 4 Ch 500 Watt Amplifier
And there is always the alpine pdx5
If you are going with JL you are going to want a strong amp to power it, the infinity and alpine would do this best.
The bostons I think I have told you about before they are good but there are other choices as well for better money.
Tips for buying, look on ebay caraudio.com in the F/S section craigslist and my favorite woofersetc.com
Sorry to talk about what you are planning just know how things go when I started. I bought lower end stuff thinking I was going to like it but I was wrong in the long run I spent more money swapping out stuff than saving and doing it right the first time. Do it once do it right.