Since Thaniel has not replied yet & I'm still subscribed, I'll break down off the top of my head what my '94 525iT project has cost:
Car: $3000
Motor: $850 (5.3L aluminum block V8 from JY)
Mounts: $200 (recycled BMW mounts, plate/angle steel for motor/trans mounts w/ welding)
Oil pan(s): $300 (GM Hummer new)
Intake, rails, car (C5) accessories: $400 (TB, MAF, AC comp, water pump, alt, BMW PS pump)
PCM: $100 (98 F-body used)
Wiring: $150 (98 F-body used)
Trans: $1200 (used T56, shipped)
Shifter parts: $100 (GM/BMW used & new)
Clutch: $400 (LS7, new, complete w/ TOB)
Plumbing: $500-1000 (includes braided lines, fittings, oil, water, PS)
Hardware: $200 (metric/special length bolts, nuts, etc.)
Turbo: $500 (New MP T70)
Intercoolers: $500 (used ATI F-body)
Radiator: $150 (BMW 540 aftermarket new)
Oil cooler: $100 (new B&M w/ fittings)
Fan: $50 (used Mark 8 Lincoln)
Cobra Hydroboost brakes: $300 (master cylinder, fittings, lines)
Large case diff: $400 (used from 7 series)
Adapters to fit large case diff: $200 (used 540 axles, carriers)
Driveshaft: $300 (new, steel)
Driveshaft flange adapter: $100
Piping for turbo log manifold: $100 (includes local welding cost)
Exhaust: $700 (wastegate, BOV, headers, pipes, muffler, flex joints, V-band couplers, more welding)
Misc: $500 (there is always something, and if I think about it some more I'll remember a few things I left out

)
Total: $11,300~11,800
I also added 850 front/540 rear brakes and a gauge panel (vac/boost, oil pressure, and volts) at a cost of several hundred dollars. This also does not take into account the labor saved by doing 98% of this myself, the auto-to-manual conversion parts, or the HP Tuners subscription I have. I'd say the above stuff easily adds close to $2000 to what I have invested w/o labor.
Time to build working a few days a week: 11 months to get running, still working out bugs when I get motivated to do so.
You can eliminate some of the stuff such as the turbo for most builds. I'm an admitted cheapskate, so I will usually try & save as many $ as possible within reason. Accordingly, I think most of the estimates are on the low end for cost.
If you took the car to a shop & said do this, I could see it running close to $30K depending on what all you wanted done and you provided nothing but the car.