I can see $800/rm. if they are using a high quality in-ceiling speaker with a back box. The price of speakers can vary a lot. Like there are $1,000+ in-ceiling speakers. So, if you are looking at a good back box, one that absorbs sound, then that may be a couple hundred bucks. Plus in-ceiling speakers that are better than average and a brand name, you are suddenly at $600 for the speakers. They have to run the wire, install the back box, then come back and cut the ceiling and install the speakers. If they've included amplification or any head-end equipment, then that easily eats up at least a couple of hours...
So, yes. It is perfectly FEASIBLE that $800 per room is a reasonable price for wiring PLUS speakers in every room. But, you would want a completely different number if you ask for them to just prewire. I had a home built a number of years ago and the prewire was, I want to say either $80 or $120 per wire. Didn't really matter what kind of wire it was. Maybe it was $80 for any wire I provided to them and $120 for any wire they provided for me. They had to do the labor, but I was actually asked to be on site the day of wiring to ensure all wiring was pulled where I wanted it. I got about $5,000 in wiring done, so about 50/60 wires or so.
So, it is fair to spend some time talking to them, and talking to the builder. While there may not seem like there is much flexibility, the builder may actually have a list of contractors it can work with on file. You can also get pretty snarky if need be when you let them know that the options are more than double or triple what you find in retail stores, let alone online.
Frankly, for years, I've used Monoprice speakers. They aren't great. They are good. They are very good for background audio at low to moderate volume. So, a decent set of their 8" speakers is under $100 a pair. They certainly compare to the $120+ models from Polk or Klipsch.
You had asked about where the main equipment location should be. This is a great question and I think people really don't get this right quite often. You will have high dollar electronics that require good access and ventilation. If you stick them into an enclosed space, then that space needs plenty of ventilation, or you will cook your gear and it will die. You also want good access so that it can be wired up and worked on properly. I'm not sure of your home design, but I almost always recommend that equipment go into a unfinished space in the basement or a closet/office with decent access and ventilation. You can do a family room location, but there will be a number of wires in use and you won't have great access to them if you stuff the equipment into a 'TV cabinet' that wasn't actually designed around proper equipment storage. Many of those TV cabinets barely have any ventilation, or none at all. So, I would look for a central location which has a lot of access.
When I suggested you be aware of in-ceiling speakers, I mean that if you have rooms overhead, you will want to be aware of them. You really can't use a surround sound system in your family room if you have in-ceiling speakers and a bedroom in the floor above and people who may be trying to sleep. So, if you have kid's bedrooms, or a family member that needs to sleep earlier, you can't use those speakers at that time. This could be a non-issue. I will say that in-wall speakers are always my preference over in-ceiling speakers. They have the same issue in that they direct sound into adjoining rooms, but they sound better (IME) and the sound bleed isn't typically going upstairs to bedrooms. But, that depends largely on the home design. Where I'm at, basements are normal, and bedrooms on the top floor above a main floor are quite common. Equipment in the basement, in-wall speakers preferred.
It is a lot to consider, but you do want to talk to the installer and potentially the builder. A pleasant conversation, but talk about the pricing not being anywhere near where you would like to be. Ask about brand names and what specific make/model of product they are installing. I will say that I do markup my Monoprice speakers when I install them... I have to. But, the final price is still less than what a Polk or Klipsch speaker would be. But, there are certainly situations where I could quickly get speaker cost up to $500 or more and really not be making more than about 10% on the materials. I could also have situations where I'm installing the cable, the speaker, the amplifier, and a source selector... and the final price is easily $800 or more per room.
OH - and for the surround sound room with in-ceiling speakers.... I would have them pull a cat-5/6 cable from the head end to the AV receiver. This way you can send audio from the home distribution system to your receiver directly using audio baluns.
I just prewired an absolutely huge home and I think it was a bit over $10,000. Multiple network cables to a bunch of TV locations along with audio prewiring in a ton of places. Maybe 100 wires or so in a very large home. But, no equipment. Equipment dramatically changes everything.
