Lowe’s sells a replacement mower blade that fits my mower for about $18 with tax. Apparently my old blade wasn’t mulching well anymore, the back yard grass was tall but with the new blade I am sure the bag had to be emptied less than half as often as with the old blade.
Just doing some rough math, even if I only mowed 9 times this season, and even if the blade saved me only 2 empties per mow, and if I replaced the blade every other year, that’s 50 cents per bag I didn’t have to trudge back to the compost pile with. I would have gladly paid one of the kids to do that, but they are grown now and no grandkid labor to exploit yet, so a new blade is the next best thing.
YMMV… Some blades could probably be sharpened but mine was pretty dinged up; sometimes I encounter a hidden rock, or log, or bicycle, or transmission in the tall grass at the beginning of the mowing season. If it is tall enough to get my butt wet when I am laying in the hammock, time to mow!