If your looking to spend 300 on an amp, go on ebay and look for Alpine V-12 M500. It puts out 1000 watts and they are alpine watts so the actual power is much higher. You may also want to look at teh MTX Thunder line of class D amps. Also, You can find a lot of 2000 and 2001 model year amps, (particularly with Alpine and MTX) on ebay that are brand new and really cheap becasuse wholesalers buy them in high volume plus they aren't the current model year so you get good amps real cheap. As for subs, there are a lot of things to take into consideration. If you want a good, quality sounding system, you can do it with 1 12" sub and a decent powered amp and still have plenty of room in your trunk to carry the groceries. By the questions you ask, I assume you are new to car audio so you may want to start small and upgrade later. I personally have 2 12" Diamond M5's running on only 200 watts each and they pump. They will be getting the alpine mentioned above hooked up this week. Also, keep in mind that subs and power to them has a lot to do with the enclosure. Large enclosures need less power to drive the speaker than small enclosures. The only reason I have 2 of the M5's is because I got them for dealer cost ($125 each) from a friend in the industry. They used to retail over $200. One of those subs will pound your car if it's in the right enclosure.