To build one at home is relatively easy and can be done under $700 depending on what and where you look for parts. I built mine under $500.
you will need
3-4 sheets plywood
1/8 or 1/4 inch angle iron. minimum 24ft for each rail
4 V caster wheels, this is the most costly and can be found at places like Granger.com, get them rated for at least 800+lbs
then you will need 4x4s to frame under the rails. Actually buying 2 2x4s and nailing them together to make 4x4s is cheaper.
you will need carpet as well, usually Lowes has left over carpet at discount or we use the cheapest carpet you can find that STILL PROVIDES some gripl
Glue the carpet to the laid plywood, then lay your angle iron directly over the outer 4x4s. All we did is toenail screws in place to hold the angle iron from moving.
Then build your cart and install the wheels, we actually bought a yard cart from TSC and removed their wheels and installed the V caster wheels.
Now this is not a competition track but it is a very good and affordable weight pull track for the house.
I ran a 4x4 directly under each rail and one in the middle of the two, then screw down the plywood directly on top.