Well there is initial cost. Grinder and stuffer and the consumable items like casings, cure and spices. Yeah, the initial outlay for the first 2 items may be kinda spendy, but they are items that will last for years and years.
Second, is the quality. Nothing on the store shelves can compare to what you make at home, nothing. You know just whats in it, where the meat came from, the spices and so on. Not fillers, bulk meat that comes from lord knows where. Its just like buying a big cryovac of top sirloin or ribeye from sams. Sure, its going to be expensive buying that much meat, but when you get it home and cut it up yourself, its actually allot cheaper. Plus, with so many sausage varities out there to be made, there is not a store around that can offer that.
The big commercial sausage makers simply cannot offer a wholesome sausage like the ones that can be at home as it is just not cost effective. Thats why they are full of fillers.
If you do get a grinder, find yourself a pork butt in the 10# range. If you do, send me a private message and I will send you a recipe for sage breakfast sausge that is not only healthier for you, but will taste fantastic. And you won't even need any casising. I promise you, if you start making your own sausage, you'll wonder why you did not start sooner.