cheapest way to get pee out of a mattress?

blot as much as you can first, don't rub. spray 50/50 white vinegar and water, blot again, then cover it in baking soda and leave it several hours (overnight is better) and vacuum it up. if it's dried in and still smells after that, an enzyme cleaner from the pet aisle is the cheap thing that actually breaks the urine down. and get a waterproof protector after, cheaper than doing this again.