If that's the case (assuming you have a multispeed bike) you can remove the casette and derailleur from your rear wheel and get a fixed cog similar to this cheapo one on amazon I found. With that you would most likely have to get a crankset (here's another cheap one)that can take a 1/8" chain or a 3/32" chain (dependent on what size cog you get) and after that your bike would pretty much be "fixed"

Sheldon Brown has a great article on conversions that could be of some help to you. I know you just want to try the whole thing out but for 50 bones, I don't think it'll be very easy or reliable. If you have any friends who ride fixed ask if you can use their bike. Or go to your LBS and let them know you want to ride fixed and they'll probably let you try one out

I truly don't know much about conversions so hopefully someone else can correct me on any mistakes or help you with your question