You can call filemaker at 1-800-252-3640 for pricing information. Usually amazon has good prices. The sale that ran last December was for version 12. Most sales are on the current version which is 12. There were major changes between 11 and 12. 12 converts the databases and then 11 can't read it. You would need to buy another copy of 11 or two copies of 12.
Thank you! Apparently I can downgrade a version 12 purchase to 11 (see http://help.filemaker.com/app/answers/detail/a_id/248/kw/license%20previous%20version) so I'm not so worried about that. I did check Amazon (UK), but the prices seemed to be the same or more than the standard. Thanks for the idea: I will try giving FileMaker a call, but I doubt they'd tell me about upcoming discounts...