It would be cheaper to buy a new one(mower) and get a factory warranty in the long run. The engines usually cost as much as two thirds the price of a new complete mower. Look in comment box below for the websites on the engines and there prices.
My Lawn Mower Engine Just Went Bang. It Had Been Smoking For A While. Is It Worth Replacing? Engine On A 6 Year Old Riding Lawn Mower (18 Hp OHV).
That is not exactly true. You can replace the engine and save quite a bit of money, rather than rushing out to buy a new lawn tractor. I bought a rebuilt 24hp Briggs and Stratton on eBay, and it cost me less than $500 with shipping included. Now, if you were to buy this engine new at retail cost, it would be over a $1000. My Troy Bilt lawn tractor was only a few years old, and still looked brand new when the engine blew, due to a faulty governor. So, I couldn't bring myself to just junk the tractor. I did some research, and looked around for the best price, and now have a great riding lawn mower again. I saved myself at least $500 by doing this.