I wish I could remember who suggested these to me, but I can't. Anyway the cheapest idea, that works very well and is much safer than any metal sand ladder or ramp is as follows:
Get a used snowmobile track (usually free or close to it) cut the track in half and you have 2 steel reinforced rubber mats with traction ribs or paddles on one side and raised rubber knobs on the other. They measure approx 12" x 4'. For storage you can roll them up, or lay them flat. They don't work very well for heating tortillas, but they also won't damage your vehicle and (more importantly) won't hurt bystanders.
Cheers
Mark