if you know the right people you can do it cheaper.
problem is than nowaday's some people will charge $500+ for a T50 for example
engine+box, 800
mounts, 200
diff, 1000
suspention, 600
exhauset, 350
cert, 450
those are just a few things you'll need. thats about $3500 right there and then you'll need brakes, clutch, radiator with plumbing, the numerous amount of beers too shout your mates
but remember, when you start it you'll end up spending WAY more... might as well set some new plugs, new leads, oil, filters, new clutch, release bearing, pressure plate and the list goes on and on and on