KVM switches in general tend to be hideously overpriced.
Though for 2 or 4 port some of the less expensive ones like a couple of the iogear models are less insanely priced.
There is no reasonably inexpensive DVI KVM that I'm aware of yet, sadly, or I'd buy one.
You do sometimes sacrifice a fair bit of video quality using VGA through a KVM. It depends on how long the VGA cables are, how well shielded, how thick the wire inside the cable is, how good of a quality of a cable/connector mating they have, etc.
If you use good quality and not too long VGA cables and are running a "server" with text consoles or maybe limited graphical resolution like maybe 1280x1024 or less you should have relatively little complaint about VGA KVMvideo quality.
If you want to run in something like 1900x1200 with a high refresh rate and small fonts, etc., well, you're pretty likely to see some ghosting, blurriness, etc.
Buy good thick shielded VGA cables and try to keep them to around 6' or maybe 9' and it shouldn't be TOO bad.
Also you might want to try to use the monitor's built in DVI and VGA connectors to hook up at least one of the PCs with the highest quality video output directly to the DVI port but use the KVM to switch the keyboard / mouse, that way at least one system will be in maximum quality.