You can buy a drop out driveline, a better rear end, and brakes for well under 5k, your looking at so many different factors such as many different displacement engines, brakes are different, rear ends are different.
Need more info on what your looking to build toove yoi a better idea on the type of donor vehicle you would be looking for.
Or simply get a 5.3 from a yard for under $1000, spend $1500 on a nice rear end, 1500 on trans setup or less, and that still gives your 1k for brakes.. Much better stuff over stock