I'm not a very successful lawn mower repair guy, but I think I saw something, maybe even before the net, with lots of new engines for 50 or 100 dollars, closer to 50, but years ago. The only problem would be being sure it would fit. They are very much alike, even the bolt holes, but maybe there are differnces. Of course you have the numbers from your current engine so maybe that's all you need.
Wait a second. This is a push mower? If it costs 250, it must have special features???