That's quite a problem you have there and I certainly feel for you.
Lowe's rents an orbital floor sander which would smooth the OSB down for you(100 grit); prime it with Kilz, allow to dry and set for 24 hours, sand it lightly again (200 grit) just to knock down the grain that is standing up from the primer. Then, you can paint with a good porch and floor enamel (I get all my paint from Wal-Mart) two coats. I used a painted floor for 12 years and, sure it had some knicks and scratches in it but, overall, it still looked pretty good.
That's the least expensive way I know of to have a new floor. If you want to get real creative about it you can get a stencil and do a border about a foot from the walls (like ivy vine maybe).