You can grind up unmedicated sow feed pellets and then add water, then form into larger chunks BUT....

The reason the chunk of lab block(or any large chunk feed) is so sturdy and hard is because it's forced through a die that shapes it. Just rolling it out and cutting blocks will give you a more crumbly block that the rodents will probably easily break apart, leading to the waste that you're trying to prevent.

Also, getting the proper ingredients cheap enough to make your own block, to be cheaper than food premade by a company would be near impossible, imo. They buy in tons, paying much less.

Right now, my rats are eating the Doggy Bag dog food from Tractor Supply. I had doubts that a dog food could work but other members were swearing by it so I gave it a shot. The rats seem to be doing pretty well on it, it's larger chunks and it's incredibly cheap.