Is it ok to mix my male cat's expensive dry urinary tract health food especially with a less expensive dry food?

First of all, dry food- any dry food - might be doing your cat more harm than good. Is your cat supposed to be consuming more water or less water? When cats eat dry food they do not drink enough water and become dehydrated. This is one of the main reasons that wet (canned) food is recommended for cats. So even if a vet told you to buy dry urinary tract health food, I would do some research to see whether your cat's medical problem could become worse if he does not receive enough fluids.

If you mix the urinary tract health food with any non-urinary tract food, you are diluting/weakening the effect that the health food will have on your cat.