I buy the cheapest hamburger I can find and mix it in with my ground up deer. It usually comes in 5lb tubes and is about 23% fat. I trim all the deer fat off as otherwise it will give the end result a gamey flavor.

I mix it about 2lbs of lean ground up deer meat with 1lb of the store bought hamburger.

The end result is about 93% lean burger. Most folks can't tell the difference.

I have a #12 electric grinder I bought at gander mountain. It shows online to be $179.99 but I bought it for $79.99 in the store on a special. I think I just saw them for that price again last week actually. I've ground up 1 elk, 3 deer, and a bunch of pigs with mine and it seems to do a pretty good job.