Well, it is a way to cut costs- that's what you were asking for advice on xD It's possible to rotate even one pasture, I have a 1 acre pasture that I cut in half during the wet season so the ground doesn't get torn up. Indie survives on half an acre just fine, and when the ground is all recovered and the grass green I let her back on it again. It isn't much, but it does last a few days and does help put on some pounds
Another good way to cut costs, if your horse is barefoot is to invest in learning about hoof trimming (it's good to find someone to help you learn hands on). Even if you don't want to do the whole thing; keeping them touched up can prolong the farrier visits. I do my own farrier work, and it saves me $30 a month- about the cost of a hay bale during late summer! It adds up.
Buy horse wormer online in bulk, the generic stuff (if it works for you) is only a couple dollars, buying a years worth really isn't that much and it's nice to always have it on hand.
If you need supplements, buy corn oil instead of expensive horse related oils, does the same thing and keeps the weight on beautifully during the winter.
Hmm... I could think of more, I'm a very hands on do it yourself person, if you have anything specific that you want to know how to cut costs with, it'd be easier to pin point and keep my poor frazzled mine focused