I sympathize. Who wants to spend beaucoup bucks on storage instead of on canvas, paints, brushes, etc. (Or food, rent, shoes for children, etc)
First, you're an artist, so think outside the box. Why must the storage center be wood? What about PVC piping?
1) is moderately rigid
2) easily available at any DIY center like lowes or home depot
3) has right angles and three-D joiners
4) is easily worked
5) is cheap
6) is light--no wheels needed--you just drag it!
7) is easily drilled through and if you don't have a drill, wop it with a hammer and nail to make the hole, and
8) you can stretch nylon fishing cord between said drilled holes...
Okay. I'm a PVC fanatic. I've used it to build boy and girl scout shelters, doghouses, spray tents for fuming antique oak, sandblasting enclosures, etc.
The point is... forget an individual commercial product: they're expensive. See what function it achieves, and do it on your own, cheaper!
If you want specific advice, contact me at firstname.lastname@example.org
ABOVE ALL: don't let your storage problems divert you from producing your art!