I checked ebay for you, but none currently worth buying. Make sure you get one with all the parts. Slitting cutters and cams, for example, go for more than it's worth to buy one without these pieces.
Do a Google search for 'Stanley 55 plane manual", and print it out when you find it. It will show all the parts so you know what you are looking at when bidding on one.
I've bought two complete ones (with only one cutter) off ebay for around a hundred bucks, but it takes some looking, and being lucky to bid when no collectors are after it.