Certainly not wasted, it seems my question actually generated quite a bit of interest.
Thank you ALL for your comments and suggestions, they were all very helpful to me.
I have not made a final decision, but I'm eliminating the framing and the metal options, which probably leaves me with foam/styrene/gatorboard.
Framing and metal I'm eliminating both on price and esthetics basis. The suggested shop (Michel's ?) just does not have the quality frames and the sizes I desire. I was considering americanframe.com, which I used before, but with museum glass, which is the only one that really cuts reflections ($40+ a piece for 12 by 18 from most on-line sources), this would easily run over $1000 for 16 full sets of frames. Since this is an abstract/experimental work and part of a single installation, I'm reluctant to use frames at all. I never used metal, but I'm afraid that the true matte might be not realizable here. Please, correct me, if I'm wrong. I also like the prints to be as close to the wall as possible, so since metal mounts apparently "float" in the air, this is not a good option for me. The price would be lower than the quality framing I was considering, but still about $700 for the set.
The foam option will be close to the wall, frame-free, true matte, and cheap, but I'm afraid a bit flimsy and hard to fix in a stable and precise manner to the wall. However at present this seems like the best compromise for me.