I pay US$40 in Seattle at a smaller local beauty parlor ran by Vietnamese women. I say this because I think they might be less expensive than others.
I am fairly hairy and it takes about 30-40 minutes to do my back.
As for what to expect here are my experiences:
1. It hurts, the pain is not intolerable but it is sharp, however it only lasts few seconds.
2. It helps to prepare your back, if your hair is long, trim it before you go. Trim it down to about 1/4 to 1/2 inch.
3. Long hair can sometimes break off without being pulled out and those will reappear much faster and sooner. otherwise you can expect about 80% regrowth in about 8 weeks. I would recommend to have it done with about 6 to 8 week frequency.
4. I don't get many zits, but my back gets a little red for about 2-3 days. You might get some ingrown hairs too. None of this is big deal as long as you apply basic hygiene. Also, depending on weather temperature and humidity, you might find your skin to develop dryness and you might feel cold in colder weather.