I agree that 30" deep cabinets are a pain to find things unless you have a special need for storing extra large stuff and, the material usage of a 4 x 8 sheet is not good. However, if you really need the 30", you can get 5 x 8 or 5 x 10 plywood, mdf or melamine panels at your local dealers who supply materials to cabinet shops and furniture makers so your usage can be much better.
My new garage will have 5) 36" wide x 7' high cabinets made from 3/4" white melamine and laminated with red laminate and thick pvc edge banding on the exposed faces and edges. One is 24" deep for larger items but the rest are only 18" deep because I am tired of stuff lost out of sight in cabinets that are any deeper.
You might want to contact a local cabinet shop to get a price on having them cut and machine the parts. Most shops today have computer cabinet programs which allow the design to be directly downloaded to the shop computerized saw or cnc router which automatically cuts the material, drills the holes for the assembly dowels, hinges and shelf clips and labels each part. The parts then go to an automated edge bander to apply any color or thickness of edge protection you want.
This is the way I went. I pick up the unassembled parts the day after tomorrow and everything will fit into my Yukon so there will be no truck rental expense to haul these large cabinets or any labor expense for the shop to assemble them. All I need is some dowel glue and a set of clamps to get them done.
Glen