Lawn mower blades can easily be sharpened for 100 times or more and usually you can sharpen a good set of lawn mower blades for the life of the lawn mower.
When you sharpen lawn mower blades you can use an angle grinder or a bench grinder and you should use a lawn mower blade balance tool to make sure the lawn mower blade is in balance.
If the lawn mower blade is off balance it can cause vibrations of your lawn mower and damage the lawn mower or engine.
Sharpen a little of the blade at a time one each side and check for balance and if it tips to one side then you need to sharpen the other side of the blade a little bit again then check the blade for balance.
Or you can pay a lawn mower place to sharpen your lawn mower blade for $5.00 to $10.00 which is not bad.
I've sharpened my own lawn mower blades for at least 50 times if I can remember properly so you can sharpen lawn mower blades several times before replacing the blades with new ones.
It's recommended to sharpen lawn mower blades every season if you mow a lot or every 2 or 3 years if you're just mowing your own lawn.