Hello from the south! Congrats on putting a sound system in your ride!
I have been building car audio systems for my cars and trucks ever since I was 16. I am not professing to be the best or a professional mobile audiophile. Classify my knowlege to be about at "educated amatuer", so please understand this is just an opinion.
There are plenty of hi-powered amps for cheap pricing. Those amplifiers are high powered and may deliver clean sound, reliable use, but sometimes unless your buying a used amp, the reason the higher pricing on most amps is because of circuitry engineering and design, and also the quality of the build.
Do yourself a favor and if you need to, save a little longer to get something that won't create such a massive amp draw on your cars charging system. This is why Kicker, RFosgate, infinity, JL or Alpine's are more expensive not necessarily because of marketing costs. They actually just cost more to build.
Depending on your vehicle the usual amperage output from the alternator for most is between 70-140amps. I know this because for the past 15 years I have been sell autoparts (business to business wholesale). On thing you can count on is all automotive manufactures won't have a alternator that creates amps that are not needed. The higher the output the more technology is needed to keep it working for more then just a year. BMW has watercooled alternators because they are running over 150 amps. So just getting a alternator modified doesn't mean you will have a unit that will last years or continue on if you decide to sell your ride. Basically leaving a problem for another soul to take care of.
I am also in the market for a 4channel amp to drive my door speakers.
I reviewed a Lanzar units and to achieve over 3000W of clean power the amp. draw was 400+ amp draw. Most wiring kits have a 100amp fuse. Speaking for myself, I would only a be ticked off person if I was replacing fuses all the time, and not getting my money's worth.
I am currently running two 1000w Dclass 2ch kenwoods. One to drive a 12" solo. sub and the other to run the door speakers. Clean I maybe get 500W(bridged) for the sub and 175W unbridged per channel for the doors.
At a volume that would have most people looking for a door handle or clutching at their ears, the amp draw is around 30 and capable of reaching 60, which is the limits of the kenwood built in fuse.
Don't get too dazzled by big numbers, and understand your hearing limitations and also the limitations of the charging system in your car.
Don't forget to spend the money on a decent wiring kit. 0/1 gauge to a distribution block and a capacitor. Rule of thumb 1farad per 1000 peak wattage. I am running a tsunami 20 farad hybrid cap. This cap shows both voltage and amp draw...so thats how I know the draw.
So my next move is a P500.4 Fosgate. Then most likely something like a P500 mono for the sub. I am convinced kicker makes the best valued speakers in the industry and when applied properly, RockFord Fosgate amps are the amp to buy. I hope this info helps. Good luck and if your anything like me, the right sound in your ride is paramount to your existence!!