SallyA ... how long it will last is just as much dependent on how it is treated/mistreated and maintained as it is dependent on the manufacturers quality...
I am going to assume you are looking at a smallish walk behind, push mower... The basic no frills mower should be less than $150... With a little care it could run for years... Those little 22 inch 5 HP, engines mounted on 4 wheels don't have a lot that can go wrong...
If you are wanting more than just a basic small area grass cutter, with some bells & whistles, expect to pay more and expect a few more things could go wrong...
Do NOT be swayed by brand names that you may be familiar with... In the lower end push mowers the brand name is only a name attached to the same mower as the next, to try to persuade you to get the other one... This time of year, as the mowing season is winding down, you should be able to find some sales on basic mowers...
Always check the oil before use, run synthetic if you can (costs a little more). AND try to use fresh fuel, containing no ethanol if possible (some places thats all you will find) not a great big deal, fresh is most important... :smile:KennyV