I think it depends on your area, back when I had a standard horse there was a lady with minis that was boarding at the same place I was. She worked out that 2 minis went in one 12*12 stall for the same cost as a big one.
Board in my area general runs 350 for full care stall or 250 for a run in and small paddock - I've seen 600 a mth for facilities with indoor or covered. And the small paddock run in is alot harder to find in general as DFW, TX is land locked, I live on the northern outskirts and that was what it still cost to be close to town but not too far out. IE I could find 200 a mth for stall and only one turn out - so everyone has to get along but it was an hour drive each way (gas prices aside) that would make it hard to go see my horse after work.
What you will probably run into is the boarding facility wants to fill the spot, the fact that your mini is going to eat less may or may not make the owner of the facility take a little bit off but alot of them see it as a stall/space and it is rented out weather its a big or small one.
I am currently looking at boarding and training my stallion for a mth or two - we are in the basic beginings of driving long lineing and while I can do this at my home. I have one acre, fairly level that is cross fenced so I could use the back 1/3 of the acre to work in but footing, not having a 'real' arena as well as TX weather making it hard to work consistantly without a covered. For my situation saftey wise I think its worth some money to have a safe enclosed arena vs a back paddock and or my street - and I think that driving adds even more dangers to IF something goes wrong it can go wrong in a big way.
Good luck
OH!
