Many different push lawn mowers use the Briggs & Stratton 498170 carburetor. If you have the time and the know-how, rebuilding it with a carb rebuild kit isn't hard. But if you're pressed for time, or if you just want a whole new carb, you can typically find a replacement one online for between $25 and $45.
However, right now on Amazon, the Briggs & Stratton OEM 498170 carburetor is selling for $20.85 -- much lower than its usual price. That's less than twice the price of the rebuilt kit, and it only takes a couple of minutes to replace the whole carb. This is the cheapest price I've seen for a brand new, OEM 498170 carburetor. Even a non-OEM Stens replacement carb at MowTownUSA costs seven bucks more than this OEM model.
If your mower uses this carb, now is the time to get one. Even if you don't need it yet, you'll eventually need to either rebuild or replace it, and this price probably won't be beat any time soon.