There 2 different type system in cars. SPL and SQL, sound pressure level and sound quality level, also are you looking it to competitions? How many subs you want to have? the sizes?
Alpine have nice system, only Type X is competition subwoofer, FI audio are nice form Q series and up. MMAT juggernaut, Kicker L7's- I don't really like those all they have is very loud sound, no quality built into it, JL w7 every nice woofer for the quality sound, RE audio only one's I like is XXX and MT series, some people don't have a lot of cash so they want to SXX series, MTX audio - those are very decent, I personal owns everything MTX in my car right now, sound way batter then the kicker audio. the 9500 series. I have the TS85 series, louder then a 12 inch L7, etc.
The amplifier you need is a mono channel class D amplifier, always check the RMS power, constant power, is the power to run for a long period of time, the peak power is where the subs hit at the highest point. Alpine, Kenwood eXcelon, Hifonics, MB quart, MTX audio, Kicker Audio, Memphis, Rockford Fosgate, all legit amplifier.
If your running over 1000 watt RMS, you need 2 awg or 0 awg wire to power the amp up, you might need to change the battery. On cars, if your running 2 1000 watts amp you might need to add 2nd alternator. Go with a single orion HCCA and one MTX thunder elite 4001D amp running this at 2 ohm, otherwise you going to blow the sub out. around 10 to 12 awg speaker wire. The amplifier itself is around 1000 dollars. Good luck, and bring the trophy home on the competitions.