There are plenty of cheap manual treadmills that can give you a good workout. The SF-T7723 Force Fitmill is quite special though. It comes with multi-grip handrails to let you run and walk in various positions. It has a 53L x 16W running surface. It has a 13.5% fixed incline and can handle 300lbs users.
You get 16 levels of magnetic resistance to push your body how hard you want. When you are done, you can fold the treadmill to get it out of your way.