I see young kids, hard one that, went through simular thing, but planning and having all bits just sitting there you could do a few hours of an evening in a decent garage. Build it up even with manifold downpipes attached and one long weekend, engine crane drop it in and then electrics. But even then you should have planned everything and labeled plug and play? I just break things down into sections brakes, running gear, engine, electrics, interior etc. Use what weekends to work on each bit and finally and much cheaper you end up with conversion?
Garages can do it quicker as there is more than one person working on it and they have ramps and tools in fairness I can see a garage charge what they charge, but like most people have said it can be done on a budget!
A mate just bought a whole VR6 for £400, it went right into his Corrado in two weekends! I think he sold the rest and make a profit it, cost him nothing in the end

Time management and having balls to do it fella!

Plus if anything goes wrong you know how to deal with it rather than trying to get the garage to fixing it?