If you can afford a grinder and can locate some fat, go for it.

Go to a butcher and see if you can buy some beef fat from them, its usually pretty cheap if they aren't using it in their own grind. If you can't, you can always buy a brisket with a couple inches of fat on it and just trim off the fat (or you could just throw the brisket in there). Bacon works pretty well to add a little extra fat, but I've tried going bacon/venison only and was unimpressed.

You have to make sure that the meat is well trimmed though. Don't leave any of the "film" on the outside and try to remove as many ligaments as possible.