You're probably looking at 1/2" melamine for 25 bucks a sheet, just make sure the thinner wood is up for the job with your rack design. 3/4" melamine around me is 38 bucks a 4'x8' sheet.

I just buy the big sheets and cut them, 17"x36" shelves you can get 5 out of a 4'x8' sheet. On their website an AP economy 4 tub rack is 225 bucks shipped. two sheets of wood would easily build that. plus other stuff like screws glue flex ect. you easily come under the 225 mark. Plus with DIY regardless of material, you can make the rack fit the space you are putting it in.