we went through a period at work of just buying new grinders once the wheel wore down, it was cheeper than buying a new wheel if you bought a cheap grinder apparently, i didn't really believe my boss at the time as he was probably being lazy and couldn't be arsed to find the right wheel for the machine itself.
Anyway point is the wheel will, ime, ware down to nothing before the motor on the grinder fails on even the cheapest machines, so when you add in home use and the fact you'll only use it once a week at the most perhaps? Then there seems little point paying more than 15 sobs or so for the basic item. Unless of course you have some specific function in mind.
I have an old work grinder in my garaeg, a very cheap one, its been there 5 years with lityle but regular use and is fine for eveything i do. Although a drill sharpening attachment would be handy it covers all my needs. Just stick a rubber pad under it before you bolt it down or it'll vibtate the whole contents of the bench onto the floor
