Both of the motors I've built have reused the stock crank. AFAIK there isn't a hp limit because nobody has had one fail.
You can do rods and pistons, use a frpp head changing kit and frpp main bolt kit, new gaskets where needed and only have $1500 into it. Machining including balance, deck, mainline, bore, hone, and ring fitting shouldn't be over $1000.
There you go, reuse your stock crank and block and you have a built shortblock for under $2500. Lots of people will tell you it's the wrong way to do it but most can only repeat what they read on the interwebz and have no practical experience.
IMO the most important part is the machining. The rest is just assembly work. Follow these specs
http://iihs.net/fsm/?dir=159&viewfile=Engine.pdf and you should be fine. Keep in mind there are no guarantees with forced induction. I'm fairly certain there are more cases of "professionally" built motors failing than the garage projects some of us do.
Ford has already put the engineering and research into what a mod motor needs to survive with boost. Examples are the Terminator and GT500. I've followed those specs and parts as much as possible and not had any problems. That means I'm using Mahle 4032 pistons with a ptb clearance of .0015", stock bearing clearances, 5w-20 oil, tty hardware, and not torque plate honing. Most of the keyboard experts will tell me I'm wrong but my experiences and those of countless Terminator and GT500 owners prove otherwise.
If I was building a super high hp motor it would be done differently, more than likely I'd use a race shop to build the whole thing and use studs with oringed heads, forged or billet crank, 2618 pistons, etc.
The most my motor has made is 674rwhp and I don't plan to take it any higher. If I had not used arp2000 rod bolts I wouldn't take it that far.
My point is that it's not that hard to beef up your motor enough for higher hp street and sometimes strip use. If your plans are super high hp with lots of track time it's best to talk to those with that kind of experience to find out what will fail and what needs to be modified in order to live.