I got mine at Dollar Tree. They were 3 for $1. I cut the ends off, zip tied the "rails" at the ends where I was connecting them, taped the seams on top and bottom and took my coroplast, covered it in fleece, added the treads (see the slideshow at the bottom) and zip tied it top and bottom to the basket-ramp. I zip tied the top of the ramp to the grid on the floor of the loft and put a brick under the end. You could probably do without the brick if you used a fourth basket.
It is a little bouncy but it is stable enough to hold the piggies. If you wanted to you could tape a paint stick (the kind you stir paint with) or a wooden ruler to the underside of the basket-ramp.
This is the slideshow on how to make treads for your ramp if you want them.
