Belt tensioner bearings

My 1995 tdi goes through a belt tensioner about every 2 years. The aftermarket cheap ones cost me about $150 each time. My mechanic keeps telling me that the bearings are not changeable because they are cheapies. If I buy the genuine part it will be even more.

I think next time, I'll buy on ebay from the UK, as we are being ripped off here in Oz.

I don't know what is different about the cheap ones but i'd doubt that the bearings can't be replaced. At the end of the day its a ferrous pulley with a bearing in the middle so
it must have got in there some how which generally means that they will come out.