Whoa, $300+ for a set of "AR" tools? Between the Dremel, the vise block, the 3 C-Clamps (that I currently use in place of a vice), the various punches and enough spare parts to build another AR, I don't even have $300 invested. You said that you are looking to build your own AR, I'm assuming that you will want to do barrel/upper work as well, so here goes.
For the Lower receiver assembly, you will want a brass punch set to punch in all the pins. A roll pin punch in 5/32 is also nice for the bolt release roll pin. You will need to have either a CAR stock wrench or a M4 stock wrench if you are installing a collapsable stock or a big screwdriver for an A1/A2 stock. Other than that, the lower is pretty easy to assemble. Refer to the
AR-15 Lower receiver assembly guide for more info.
For the upper, you will definitely need to have a receiver block and a barrel wrench. You can get both from Brownells or Bushmaster. Barrel blocks are nice for installing/removing muzzle devices, but you can get away with two blocks of wood. A set of headspace gauges are nice for confirming proper headspace, but not necessary if you buy name brand components from reputable vendors. Oh, and you will need a vice, the bigger the better. Refer to
FALARAK's link for info on working on the upper, installing a free float tube, etc.
Hope this helps. Also, it shows that you are in GA; if you are in the metro Atlanta area, and need a tool, post it on the hometown forum. I have tools that I would be glad to share, as does a couple more local ARFCOMers.