Again, just a possible thing that could happen and not a definitive diagnosis.
Usually caused by damaged/missing teeth on flywheel /starter gears which causes the statyer not to engage properly and produce a grinding metallic (somtimes ringing-like) sound from the flywheel. it can also be caused by a bad starter solenoid that also does not provide full engagement of the gears.
If the starter or flywheel gears are damaged, it will not be a cheap fix as you might need to replace one or the other or in some cases, both. I think most, if not all starter solenoids today are integral to the starter assembly and will most likely mean that you will need to change out the whole starter when it goes bad, so not cheap to fix either.
Not sure if a bad battery might also cause the solenoid not to do its job but if it means it's just a bad battery, not providing enough volts/amps to the starter, it would be an easy, cheaper fix. I'd start with having a load test done on your battery first to see if that might be the problem.