Here's my solution, and it cost $15 and less than 30 minutes to install:
The bins came from Big Lots, cost $3.50 each, latch together for stability, and fit my Scamp
closet perfectly. The bottom bin rests on an old plastic crate that I inverted and notched to fit over the wheel well. The whole stack fits so snugly that no permanent attachment is needed, but I used one tension curtain rod to hold the bottom bin snugly against the front of the cabinet since the closet is about an inch deeper there.
They have worked really well. Nothing falls out and everything is visible and easily accessible. They probably wouldn't work for heavy items, like canned goods, but I prefer to store heavy stuff low and forward (under the front sofa).