$40 would be a good price to just clean it, and that does not include removing the valves. If anyone is just charging 40 beware, they are likely just going to clean it all assembled and say they did a valve job.
When deciding to either pay someone else to do the work or doing it your self, just remember, if its really not your thing to do mechanical work and don't know for sure what your doing, and saying nothing about your time spent. Having it done by someone else most always has some kind of warranty, doing it yourself does not. If you goof up something its on you, the shop does it it's on them.
