I'm a little cornfused over what state your aerial is currently in. Is it still a loop, or now is it an end-fed length of 275' wire?
For receive, you can forget the balun altogether. Really. If, however, it makes you feel better to use one, go the cheap route and wind 10' of coax into a randomly wound coil 6-8" in diameter right at the aerial feed point.
If it's now a random wire, no balun is needed, as it is not a balanced aerial. Better to run 50' or so of a ground wire (along the ground) soldered directly to the coax.
In the end, if you don't have one already, save up your shekels and get yourself an "antenna tuner". MFJ makes some decent ones for cheap, and they can be found on Ebay and Craig's List (or your local ham fest).
Or, you could <gasp!> build your own.