Depends on the speed as it will need a roll cage for under certain times.

Just need to start with a cheap light glider (no running gear)
4k in batteries, 4k in controller and misc, 3k on motor, direct drive to Currie all alloy housing, Currie/Strange carrier and 4.6 lsd centre and custom tailshaft 4k.

For under 15k to be serious you have a lethal Porsche killer and uses a couple of cents of electricity per run.