I made some.
I purchased 3 8' 2x10's
One of them I cut in half, or about 48". These were the middle sections.
I cut the other two to create a 36" and 60" piece
I then used the 60" piece as the bottom. Then the 48" piece and finally the 36" piece. I had some 2x4's lying around, so I cut them to fit the top and act as stop at the end of the ramps.
I just nailed it together, and it has held up for over a year now. You could probably use bolts if so inclined, maybe some wheels at the end to make it easier to move around.
It cost me about $20-$30 and about an hours time to build them.
And some shots of the car up there:
TB