I've got a 4-to-1 video switch box for Macs. It's a metal box with a four-position dial switch on the front, and the back has four inputs and one output; all are the old-style 15 pin D-SUB (DB-15) connectors (female). Use it to run the video from up to 4 machines to a single monitor. Not sure of the specs, what resolutions it'll support, or even the manufacturer. No labels or docs on it at all -- just a plain beige box -- but I do know it works. It was used on a bank of servers until a while back, until it got replaced by a full KVM switch. I've had it open, and it's just a switch with wires passing between the connectors; my guess is that it'll support whatever resolutions the video card supports.
I've got some photos on my Picasa album; have a look if you like.
How about $20 shipped (in the lower 48 states)? If that's too much, make me an offer.
Somebody is bound to ask, but sorry, I don't have any cables for it. I know two or three that were used on it before were snagged from dead Apple RGB monitors; some of the older ones used a detachable cable that had male connectors on both ends. Worked perfectly with this box. I'm sure cables could be cobbled together from cables scavenged from dead monitors.