I've been qouted a price of EUR 85 for 18x24. I'm not sure whether this is the general price.
Another option is dibond + gloss finish. Need I say more that it involves pouring epoxy resin and a blow torch
http://www.youtube.com/watch?v=YUboGu2WiQ0
Notice that not all paper is suited for this due to the use of whiteners, inks used etc.
I forgot to mention that it is possible to frame without a mat and stille preserve the print. This is done by placing spacers along the edge of the print so it doesn't touch the glass.