In my experience, price guides for glass are just as useless as price guides for other antiques. More useful for a beginning collector is a good picture book, and Leslie Pina's Italian Glass is one of the best, although the experts on this board have stated that many of her attributions are dubious. The problem with some of the other guides is that they show mostly museum quality pieces that are out of the range of most collectors. One side note - collecting books, especially monographs, can be worthwhile. They shoot up in value after they go out of print.