lowes sells the waren pro grinder for 100 bucks , i have had one for 4 years and ground up quite a few deer , it's not a big grinder and you have to feed it slowly , but it does it's job.
deer meat is very very lean , alot of people add pork fat to the deer to make it have a bit of fat, i seen anywhere from 20 to 50% fat added , i personally get it right around 25-30% sometimes i even add a bit of bacon to it.
pork butts are great to mix into the deer burger.. and if you know a butcher you may be able to get some of the fat trimmings they have left after they process the meats.it's another cheap alternative.
here's a cheap grinder...
http://www.harborfreight.com/cpi/cta...emnumber=99598
don't really know how well it would hold up though.