I haven't changed money in the hotels but the Banks do a good exchange rate. We used the First Investment Bank in Bansko. There is a young man that speaks English there. Much safer than using the cash machines in town.
Havn't been to Bansko, but have been to Pamps a few times. (Off to Bansko this year in Feb) You will be able to change money at the hotel - but I think you will find the best rate of exchange will be at a cash machine - at least that is what we found when we were in Pamps. Do a search for "exchange" on the discussion board here and take note of warnings regarding money exchange.
I changed money there back in March - they didn't charge commission and the rate was pretty close to the official one.
There's a cash dispenser near the ticket office at the bottom gondola station too.