There are complete feeds out there, many manufacturers make them. They are balanced to meet all the nutritional needs of a horse. BUT! Horses hindgut functions best when it has at least *some* long stem roughage - stems being 1-2" long. So some horses do better when you use soaked hay cubes in addition to a complete feed.
There are LOTS of hay cubes out there, and they can be pretty inexpensive. Alfalfa tends to be the most expensive cube, so look for another variety with timothy or other grass hay in it to be cheaper. Some people feed the cubes dry with good results, but I have seen too many horses choke on dry cubes.... So all of mine are soaked now. Hot water soaks them faster, and makes it yummy in winter. Slowly introduce the soaked cubes though, some horses have to aquire a taste for them. Locally (southern MD) I pay from $13-21 for a bag of hay cubes, depending on variety and manufacturer.
There is also "chopped forage" which is a mix of chopped hay and usually molasses. It is a good option also. Cost locally is usually under $15 for a 40lb compressed bag.
Some manufacturers make a "hay stretcher" feed - you can look into using that...I've never used it, so I don't know what it costs of how it works best. But I know a lot of people in OK were using it during the summer drought 2011.
Also, call EVERY manufacturer that supplies your area. Talk to a rep, explain your situation, and you might just get several couponms for free bags. You won't want to switch cold turkey from one manufacturer to another, but if you ease into any change, then you will be fine using free bags of different manufacturers.
Another cheap option (if round or mid-square bales are cheap in your area) If you can get someone to deliver a single round bale to you, you can actually make that ONE bale last 2 months or so, depending on how big it is. DON'T put it in the pen with your horse - set it somewhere outside the fence and PEEL off what you want to feed her each day. If you only feed the amount she needs to eat, she will clean up every bit and not waste any. Cover it with a tarp if it rains, but keep it uncovered as long as it isn't raining. It won't mold. If you do find any mold spots in it (usually you'll find some on the outer layers) just set them aside and don't feed them. But most horses won't eat any moldy parts if they do encounter them, as long as they have something else to eat.
