Dolomites: must book hotel/guest house in advance?

Do we need to book a hotel or hostel or guest house in advance in the Dolomites in early July? We are assuming that we can take a bus into a valley village or town and look for "room available" signs. We plan to spend most of our time in refugia in the mountains but we have to start in the valleys. I am aware that one can book some places on the web but the places that can afford web sites seem expensive. Any advice appreciated.
Thanks, Lomad

early July is super high season for tourists from NEurope, so Yes.
I think nowadays that most places (except SOME 2 room B&B) have homepages (own or througt the local tourist office or some cooperation) - maybe you just are seeing the normal prices?

Bjoern, You motivated me to dig deeper into the internet sources and I found many Hotel Garni and B&B in the 25 to 30 euro per person with breakfast in Val de Gardena. These prices are hardly different from the mountain refugia where we hope to spend most of our time.
Thanks.

Fine - I would expect that the major part of places would be in 50-100€ range for 2 - with the best places (luxury Guesthouses, "B&B on a castle" or very good hotels) up to 200€ - seems that you have found these prices. Were not aware if these were what you called expensive in original posting.

Bjoern, "Expensive" was the idea that most places on the web accepted only 3 to 7 day minimum reservations when we wanted only one night before entering the mountains. On the Val Gardena web site I found places that would accept one overnight reservations at a very reasonable cost (the lower end you suggested...for late June and early July).
Also, I am beginning to understand what "normal" prices are! So, Thanks again!