I keep my eye on the market all the time, and I agree that it's definitely not like it used to be. Lotta folks out there are wanting $2-3k for a running stock-ish 5.0 motor. At those prices I'm afraid of getting ripped off. In the old days, you could pick up a $500 engine to swap your stuff on, and if they lied it was just a bad day. Hell, I had a friend,
@Ford Moore swap my old turbo kit and X-heads onto a $50 junkyard 302, smooth out a damaged piston, and rock on with ~450rwhp not really caring if he blew it up. Honestly, that's the way to do it. No waiting months on a build, having to navigate the whole aftermarket catalog, and then worrying that every little tick or noise is some expensive engine killing catastrophe. At the prices a 'new' stock build is going for, it really does put you in a spot where jumping up to holding out to find an aftermarket block (Dart, Boss, World, R302, A4) is pretty reasonable.
You can still get stockers on the market at reasonable prices, though. Here's one that's frankly hard to believe:
If it comes with everything in the pic & it all works, $800's a smokin' deal. Getting to 500 rwhp in a fox is about the most you'll be able to do on a budget. I think one of the best bang for the buck combos out there is to slap on any aftermarket cylinder head you can get your hands on with the cheapest quality explorer intake you can find to get to what would be a 230-250 rwhp NA build, then buy a 340 lph pump, 42 lbs injetors, & a quarterhorse or Tweecer, and then slap a turbo kit with an intercooler on there and run up to 15 psi on 93 octane to max out the stock block. The beauty of it is that you don't have to worry about internals/displacement/cam etc... You won't get nervous about problems or running it hard. You should be able to replace all the parts for cheap and run that car deep into the 10s on that kind of power.
You can find rebuilt ones that'll cost you more, but I'd worry about how they were put together, or whether they were even actually rebuilt. Example: