have owned an earthquake 10" and 12". (sold the 12"). also, RBH 10" aluminum sub. (sold that, too). as far as homemade subs, i made an active 10" titanic driver with a plate amp from madisound, as well as a passive 12" peerless driver with an external ashley crossover.
the peerless 12" was the fastest of the bunch, followed by the earthquakes. an active sub will be the most practical, but my passive peerless sounds fantastic. thick, fast and punchy, not boomy, like the rbh tended to be. i would say it really depends on the driver. you can make an incredible sub for under $500 - most peerless and titanic drivers go for less than $200 and a plate amp w/crossover from partsexpress or madisound will run around $150-200. a 12 or 15" SLAPS earthquake driver will only cost you $100-150 as well - i just got a new slaps 12" for $75. you can then either buy a pre-cut box or go to your local lumber yard and get them to cut down a 4'x8' sheet of 3/4" ply to your exact specs ($60). put a few coats of poly on it and you'll get a MUCH nicer wood grain and a more unique box than the black boxes that partsexpress sells and you'll spend less $.