Most hotels, shops, restaurants, cafes and galleries in Oia are situated along a pedestrian-only walkway Unfortunately this doesn't include Aspa or Olympic. Any hotel in that part of the village is going to be quiet, especially the further down the cliff you go. Oia is small, so within that area nothing is an inconvenient distance from everything else, certainly no more than 15 minutes' walk from one end to the other along that pedestrian path, as long as you're not seduced by the view or doing some window shopping. I challenge you NOT to stop!! ;-0
If you want a caldera view there aren't many hotels along that path that don't require some step-climbing. Only Old Oia Houses comes to mind right now, House D if I remember correctly. That said, none of the ones I listed is so far down the cliff as to challenge you to any serious degree, unless you have some sort of respiratory or mobility issue.
As for what your money will buy in October, I don't have a clue. It's up to you to do that research yourself using the filter system at www.booking.com as well as the individual hotels' websites to find room rates. The good news is that by October prices have mostly dropped to low season rates, so you shouldn't have a problem finding something nice.