If you are patient and don't mind buying small, the most economical will be buying from a tree seedling nursery like Cascade Forestry or Musser Forests. I checked Cascade and website shows they are sold out of most. Musser has them in the two smaller size but the pots are sold out. Google 'tree seeding nursery' will bring up some links you can check.

Otherwise, I would investigate by phone calling local nurseries.

I just saw some at Menard's for around $60. I haven't ever planted any trees, so I'm not sure on the quality. I am planning to tackle that project this summer. I think I'll do a post to ask everyone's expertise. Anyway, the Service Berry tree was one that was recommended to me, sounds like it is a great tree for all seasons. Twin City Nursery in White Bear Lake seems to be having a great sale right now too. I stopped in to check it out and they were really helpful. I think their website is twincitynursery.com. Good luck!