Right now, I have:
$1200 in core, roughly running bike CB750K
$500 for the original shop adjustment of carbs, which they half-assed
$220 in "junkyard" parts including (Front and rear wheels, front dual disc brakes, front forks, tank, rearsets, front fender, brake calipers and lines, triple trees)
$220 for brake caliper rebuild kits, caliper pistons, starter cover gasket, valve cover gasket, carb float bowl gaskets, GP grips, front brake pads.
$40 so far in rattle cans
$100-200 in beer, snacks, cigars
Countless hours searching online for parts, both new and used.
And I've still got another $500-$800 to buy, and haven't touched the internals yet... Only because it runs good, just had horribly adjusted carbs.
Basically, with a half-decent running bike, you're looking in the $1500-$2500 range AFTER you have bought the bike. This is of course if you have decent mechanical skills and access to a salvage yard or bike yard of some kind. And of course tools if you don't already have them. I probably have another $200 in tools, and I work in a machine shop. Had to buy all new stuff in metric sizes.