It depends on where you want to run it. I have a pile of dirt in my yard that makes a hill. If the hill was steeper, I'd build the cheaper creeper. Alas, my hill is mostly bumps, so I use a truck that jumps :tong
I noticed you said "build" but I saw someone on another forum that was selling their Creeper and some stuff.
If you think you'd be interested I could get his email or PM you what's included and the price.