What kind of volume are you thinking about?
Adobe does have such a thing as the Acrobat Distiller Server: http://www.adobe.com/products/acrdis/main.html
but it is looking to convert a postscript file, not start with the raw document. And yes, it is pricey: $5,000 US for 100 registered users, and $10,000 for unlimited.
Getting into postscript is going to be the kicker. I don't know of anything that can take all those formats and export them into postscript.
Maybe you should make your users do that part, and upload the postscript document? From there it looks easy and cheap.
Generating a postscript file on windows is as easy as having a postscript printer driver installed (even if you don't have a printer for it) and then printing to a file!
