I know this is where the pro builders and miners are, so what would it take to build a rig which can get over 10,000khashes and could it be done for under $5000?
As others have mentioned, 10 Mh/s (LTC) for under $5k won't work.
10 Mh/s is about the power of 17 HD 7950s (at their average expected hash rate of 600 kh/s each), which cost about $300 each, so you're looking at $5100 just for the graphics cards.
You would need at least 3 motherboards, 3 CPUs, 6 PSUs, 3 flash drives, 17 risers, and 3 milk crates, in addition to the GPUs. Plus shipping, and potentially taxes. So, another $900, give or take. Note that getting more than three or four GPUs working on a single motherboard takes will require research to figure out exactly which components will definitely work, etc. It's easier to do if you limit yourself to 3 GPUs per motherboard, but that'll increase the cost another few hundred dollars.
$5k won't work, but $6k-$6.5k will do the trick. Or you could drop your target down to 8.4 Mh/s, which you might be able to get done for around $5k.