Just some thoughts. Search craigslist, put a wanted ad on it, or in the paper. Call local thrift stores and put out a request - grain mills are exactly the kind of expensive appliance people buy and use once and a lot of thriftstores will keep a list of people who want specific things. Consider multipurpose solutions, I remember Vitamix having a grain attachment. Expensive, but then you have an excellent margarita maker too!
Feed stores are an excellent place to buy bulk grains. I grew up on them. Anywhere you buy them though you have to be aware of bugs. If you freeze the bags for 2 or 3 days when you first get them it will help the bug eggs not hatch. (Yes, whole grain has bug eggs in it.) Then use it fast, making sure you store them where bugs and mice won't be able to get at them. A great idea is to sprout the grains a day before you make your breads - supposed to be more healthy.
For flax seed eaters - about 5 years ago I would buy 50 lb bags of flax seed for $30. Most of it went to my chickens, but I used some. From what I've read about flax, I suspect we actually absorb the nutrition better through eating the eggs of chickens fed it, anyway. Don't grind it for birds, and don't sprout it - it makes a gelatinous mess!
Lark