Judy, I know this seems like an odd question but do they want steins that they will actually drink out of or ones just to display? I ask because that will make a big difference in cost.
If they are for actually drinking from you have many options (like previously stated, Hofbräuhaus, Weihenstephan, or Andechs outside of Munich). Also, if they are for actual drinking, if they don't have a "top" to it, buy them a Bierdeckel to put on top of it. I bought a wooden one at a fair at the Olympic Park and I use it all the time with my various Krüge.
And the suggestion for visiting a flea market is an excellent one. I don't know where they are in/around Munich but almost all the flea markets I have been to someone has been selling some type of stein (both fancy and ones to drink from).