I'm not sure which "5000 watt" amp you're looking at, but their 5000w MAX amps are actually about 2000w (rms) amps. Perf Tek isn't a highly respected company. If they are actually capable of 2kw that would be a really good price at $270, which would make me think the durability of the amp is probably questionable.
The best budget, big power sub amps IMO are the Brutus amps from Hifonics. The bxi2010d is around $350, the 1610 is about 300, or you can get the older models (08's) a little cheaper.