Depending on how well it's running when you buy one, it may take several hundred just catching up on neglected maintenance and the like. I'm planning an RB swap on my '77 280z, and plan on a bare minimum of $8500. That's including motor, refreshing said motor, drive shaft, mounting kit, inter cooler, GReddy intake, gauges, big brake kit, you get the idea. This stuff isn't cheap, and it's not until you find all the problems the previous owner doesn't know about or tell you about when you buy it. It's a long haul project, if you want something fast tomorrow, buy something new. Cheap, fast, reliable, pick any two.