Military volunteer needs a good working Robot Vacuum, Roomba type - $50 (San Diego)

I do Dogs on Deployment, taking care of military members' dogs while they are out to sea or deployed.
Right now I have a doberman who is wonderful but sheds a lot and I need to deal with the hair.
But as this is a voluntary program, and I don't have a lot of extra money to spend, I'm hoping somebody can give me a good deal on a vacuum that will help keep my place a little cleaner during this 6 months deployment.