There are a couple of ways to get around paying $300 for a set of coilovers:
Here are step-by-step photos using stock shocks and overload springs. Be careful welding to gas shocks; only weld to the thick metal at the cupped ends of the shock (at or below the knurled factory weld), never to the body. Don't get them hot. Weld briefly, then dunk them in cold water for a bit.
Another way to make cheap coilovers is to use a stock set of Monroe Load Levelers coil-assist shocks. Remove the anemic 2 1/4" ID springs and replace them with stronger
2 1/2" ID springs by fabricating simple adapter rings. This way is more expensive ($125) but the shocks can be disassembled to change springs. Sorry, no photos.
I've got about 350 miles road-testing on these currently. So far, so good.