If you want to pick up a used LS crank and rods, they shouldn't cost all that much. My guess would be a couple hundred max. With a stock B series bottom end, and good tuning, you can run up to 14lbs of boost. If you want to be more conservative, I would stay around 10lbs if you're not sure about your tuning. If you want to run forged internals, which would be a good idea if you're going to have the bottom end apart anyway, you would definitely be good for 14lbs of boost on stock sleeves with good tuning. We're talking large injectors, high-volume intank pump, a good standalone, and dyno time. Again if you're unsure about your tuning, keep your boost level more conservative. Of course the next step is ductile iron sleeves if you want to run high boost. It's not bad to turbocharge an ITR, but there are more hurdles to get over. ITR cams have a lot of overlap, which is counterproductive to boost, but you can just swap some GSR cams in and be fine. ITR pistons also produce a higher C/R which, when mixed with boost, is more prone to detonating. To remedy that without having to open up the bottom end, you could just use a thicker headgasket to lower C/R a bit. In any case, tuning is the key. Some people run moderate boost on completely stock ITR's with absolutely no problems.