Costco sells 88% lean ground beef at $3.99 per pound. Mixed two parts elk or deer (which properly cleaned is 100% lean) to 1 part ground beef yields a mixture which is 94 % lean and frankly....tastes darn great. It also does tend to extend your yield a bit. To tell the truth, the other options (including suet) sound pretty nasty.
Lloyd, all I can say about using suet to add fat content to venison is, don't knock it until you've tried it. I felt the same way about it when I decided to try something that would hopefully make a better tasting burger than venison mixed with fatty pork. I kept thinking about my 5th grade teacher telling us that she hung out chunks of cheap suet in the winter to feed the birds, so I figured it must be basically garbage. But then I learned that it is a high quality fat that forms in the same tenderloin neighborhood as the very best cuts of beef, near and around the kidneys. Slaughterhouses and butchers don't waste it. They sell it and use it for kielbasa, sausage, etc., so you have most likely already eaten and enjoyed it. I tried it in my ground venison, and never regretted it. My kids liked it so much in venison burgers, tacos, chili, meatloaf, etc., that they would actually be disappointed if I didn't get a deer. Surprisingly, suet is even used in pie crusts and pastries.
https://www.seriouseats.com/the-nasty-bits-baking-with-suethttps://discover.grasslandbeef.com/blog/what-is-suet/I agree that the Costco ground chuck is usually good stuff. I'd imagine that mixing it with elk or deer in the ratio you describe would be good. It might even make ground Canada goose meat somewhat edible.
