Very true!
If you look at my rack you'll see those shelves with the 3 sub-adult tubs...well I got those at a local Deals dollar-type store. Although they're 6 qt. tubs, they are lower in height (4") than shoebox tubs and have a wider surface (ground) area of 10" x 13.5". Finding a size tub like that was difficult, but when I did find them I bought all they had.
Overall this rack idea was the best inexpensive option out there. I only hope that Lowes continues to sell these shelving units and not decide to change styles unexpectedly. I had found a shelf unit that was almost identical made by Plano which was sold here in the midwest by Menards. They're sturdier and cheaper ($18.95 on sale) units, but the undersides of the shelves, the side that you glue the Eucaboard to each had 3 'ribs' that protruded about 3/4" beyond the lip that you glue to. Sure, you could probably trim it with a saw or tin snips, but that would have been 33 cuts for the tall rack I made, and I was running out of time with babies due to hatch!
If anyone has questions about building this DIY rack, post them here and I'll do my best to help!