Multisite Install - But Single Site Migration

I've got three servers. One's for local dev, one for staging live testing and the last is the live environment.

Assuming I have all the domain / server stuff in place, what's the best way to migrate a single site from one server to the next.

Currently to go from Dev > Staging I'm doing an entire database export and SVN of the whole project. I need a way to just migrate a single site and everything within it as needed.

Also important to note that the url's are slightly different ie; mywebsite.dev vs sta.mywebsite.com vs mywebsite.com

Have you got a suggested plugin or solution for this. I suspect it's a common one for multi-site users.

Thanks.

Jay
CompuMatter