I've found that at the coarse grits, it doesn't seem to matter much to me, anyway, at the 36 or 60 grit range.
It's after that where things become 'important'.
As important as the belts are the platens and variable speed grinders.
My most important belt upgrade has been to the Gator 300A, which equates to an 80 grit regular belt.
Even though they're about 8 dollars, I'm now on my 9th blade with the same belt, whereas, prior to this I was using a new 120 on practically every blade!!
So, you are correct, cheap belts are VERY! expensive.