Depends on how good your beer store is. I was hitting up Binny's around Chicago for awhile to collect some flip tops. They generally had some to choose from in the import aisle. Mostly hefes and dunkels in half liter bottles.
If I remember correctly, look for Kapuziner or Weihanstephan. I want to say they were $3-4 each so not exactly cheap, but at least they came filled with good beer.