That is a freewheel hub, you can remove the freewheel and screw on a cog, then use a BB lockring and a little loctite to keep it on. Some do not like to do this but I have used this setup with no problem and you can use it to decide if you enjoy fixed enough to spend some real $$. You can also get a BB spindle and cheap crank arm for $20. Keep the front brake and ditch the rear. Keep the old bars and throw some cheap tape on there. I bet you can make this a rider for $50-60