If it has horizontal dropouts (and it looks like it does, you can do Single Speed without a tensioner.

Page down a bit on this site for a picture of dropouts, but ignore the suggestions about going fixed gear unless you are really looking that way, then it requires more than a single speed would.

https://www.google.com/url?sa=i&rct=...22397985087401

You can possibly convert for the price of a new chain if you aren't picky about gear ratio. Put the chain around the middle cog in front, and over the rear sprocket that lines up best in back... ensuring the chain is the proper length and ride away. I would probably use a 5-8 speed chain (they are all the same width).

It lacks the "cool" factor, but it could work for you.