Larry Ashley made a custom decal for me and the cost was very
reasonable, _much_ less than what you were quoted, with good
quality and rapid delivery:

  Larry E. Ashley
  Decals For Pianos and
  Publisher Pierce Piano Atlas
  Phone 1-505-296-5499
  Fax 1-505-323-0252
  http://www.PiercePianoAtlas.com/ 

or go directly to the decal page at
  http://www.piercepianoatlas.com/decals.html 

I don't know about mounting on back of glass, but he seems to be
very knowledgeable and very pleasant and easy to work with also.

Larry Claus