Building your block internally won't leave you enough cash in your budget to put together a decent turbo system... unless you go with a junkyard setup, and I wouldn't push one of those hard enough to justify strengthened internals.
I would just get a leakdown test and compression test done to make sure your engine is healthy, and if it is- buy a bolt-on turbo kit (or put one together yourself), then get the assorted electronics you need for monitoring the system (gauges) and to get a little more push out of it (boost controller, turbo timer, tuning devices).