It depends on a lot of factors. I got a complete running, driving 96 explorer for $1100. That gives me an engine, transmission, wiring harness, ecu, dash, radiator and instrument cluster. And a lot of little detail items along the way. I'm hoping to part out what's left and recoup most of that $1100. I'll probably have another $1500-$2000 in other parts along the way. So, for somewhere between $2000-$3000 or a little more, I should have a complete project. Fingers crossed. Also, mine is a 4x4. That does add to the cost and complexity.
I had a line on a complete 5.3l LS with transmission and transfer case. Asking price was $1100. I would have been using an aftermarket ecu, wiring harness and digital dash, roughly $3,500 minimum for that stuff. There would have been more fabrication getting it to fit and mount up to everything. I was looking at a >$5k project that I didn't want to pay for.
Everybody's project will be different. It depends on what you start out with and what you want to accomplish. Get a lower mileage donor than mine (251,000) and you may not need to freshen up the engine as much. Or have someone hand you a free LS motor complete with transmission, wiring harness and ecu and you can go that route a lot cheaper.
Don't forget whatever extra tools you'll need to buy or rent. I already had most of what I need. I bought a transmission jack, compression test kit with extra adapters, vacuum gauge, borescope and a fancy labelmaker that will print heat shrink wire labels because I'm doing some extensive wiring modificstions marrying the Explorer dash into my 93 Ranger.