Most of the shelters and rescue organizations around here charge somewhere in the $75-200 range. This typically includes having the animal altered. I would expect any type of reputable shelter or rescue organization to either alter the animal, or make you sign a statement that you will have the animal altered.
As far as the vet fees, it varies. We use Banfield for all of our pets. They are affiliated with petsmart, and there is one in most (maybe all) Petsmarts. We have their wellness plan. It basically amounts to pet health insurance. There is a price range, there are usually 3 levels of coverage you can get. There is also a puppy plan, and that one includes having them altered. I think the puppy plan is about $25 or so a month for a year, after a year you switch over to one of the adult plans, which I think run $20-30 depending on what level you get. These plans cover all of their shots, heartowrm testing, routine deworming. They do some tests that most people probably wouldn't pay extra for, like eye pressure tests. If you need anything else, flea prevention, further tests, emergent care etc, you get a discount. A few months ago I had to have a small tumor removed from my dog, it was going to cost $1200. They let me upgrade to a higher plan, and it cost something like $150. We also really like the care they give our pets. We also like knowing that if something happened when we were traveling, there is usually a Petsmart around.
I hope you find a wonderful pet that fits your family!