I cut my own up for the most part, but once in a while, if I'm busy with other things or for the convenience, I'll have one cut up for me. Cost really depends on what you want them to do, from a simple break down, wrap, and grind, to make (and cure/smoke) sausage.
I've worked in a couple commercial sausage kitchens. In my opinion, it is a substantial investment to get what you need to make sausage (grinder & stuffer-or a combo unit, smoker (unless you are just making fresh sausage)), and then there's a learning curve on making good sausage. Plus, when you go to make it, you will have to purchase certain supplies (spice, casings, beef/pork fat to mix in). So basically, what I'm saying is unless you want to make sausage as a hobby, it's not necessarily going to be a good investment from a money saving point of view. It takes a long time to recoup the investment (unless, I suppose, you make a very large quantity each year).
I prefer to cut mine up and take my deboned meat in to a sausage maker to have sausage made. The investment on cutting equipment in my opinion makes sense financially. All you really need is a couple good knifes, a large cutting board, some wrap, and a gambrel is really nice. A vacuum packer is a nice addition that will save some meat in the long run, but it is a luxury (I use mine for more than just game). I also have a dehydrator, which I use to make jerky out of thinly sliced pieces of meat (let a chunk sit in the freezer for about a half hour befor you slice it and you'll be able to slice it thinner).
Cutting it up and bringing meat in to a sausage maker has the added advantage of letting you pick your sausage maker. Again, IMHO, most guys who cut up deer aren't as good of sausage makers as guys who make sausage as their job. Many of these guys will only take deboned deer (including the 2 i worked for).
Cutting it up yourself isn't that hard, theres some good videos on Youtube. Good luck.