Reading the xml file and using the data to trigger tweets through the twitter api is not too hard to pull off.
As far as converting xml to rss, RSS is a form of xml. It would be fairly easy to read in a camsite's xml and put out a valid rss feed.
I am not sure off the top of my head how long it would take but I would probably charge in the $300-$500 range to do something custom on that. It would be a pretty barebones implementation though. If you wanted a complete admin panel and such it would probably be more.
I am expensive though and you could probably get it done more economically. I also will not be held to an off the top of my head estimate. I would want to look at it a little deeper to see what you really wanted to do before we finalized any kind of price..
It would be an excellent project for a beginner coder to learn handling xml in php and using the twitter api or it might make a good group project if someone was wanting to go that way.
just my
.