Welcome and it sounds like a big fun plan to be sure. Inexpensive turbos can be found all over the place from lots of manufactures for around $300-500. 5.3s make for great swaps. The 4L60e will be a ticking time bomb. I would suggest getting the 5.3 swap done and waiting to get the turbo kit built until later. You will be very surprised by the power in a stock 5.3