Assuming you've got the supporting modifications for your built cylinder head -- intake, header & exhaust -- the next logical step would be nitrous oxide injection and the requisite fuel system upgrades.

Zex builds a nice dry nitrous setup good for 55 whp when jetted conservatively. Combined with a bottle heater, opener, purge kit, fuel pump and a set of [colder] sparkplugs, you should come in under $1000 by a fair margin.