Most processors charge around $3 a pound extra to make trail bologna, jerky, smoke stick, ect...This can really add up.
Sausage takes up very little extra time to make. The things you mentioned include extra time for drying, smoking, curing, or whatever.
I helped a butcher process deer for eight years (during the season). He was extremely picky about the amount of gristle and fat from the deer that went into the grinder. Most of the bigger processors figure time is money, and trim nothing from the scraps. Venison fat has a very gamey and bitter taste, and does not freeze well at all. When I do my own sausage with my deer, I trim off every bit of fat and silver skin.
I buy what the butchers call "picnics". They are big pieces of cleaned hog fat with a little meat left on them. I cut these up. I weigh out 10 lbs of cubed and trimmed venison scraps, and add three and a half pounds of the cubed up hog fat. I add my seasonings, and let it sit in a tupperwear tub overnight. I then stuff it into natural casings with my sausage stuffer, freeze it for an hour or two, and vacuum pack it. I have a few of my neighbors save me those styrofoam meat trays throughout the year, and pack the sausage on those.