Not a real problem to do, as long as you have shell access. A bit more problematic for non-shell access.
I've done it a few times. Depending on the size of the database, it takes about an hour to do an install and make sure it works. Sometimes it takes some tweaking, which can add a bit of time.
If you've done any customizations, that means possibly more time, or longer to check it.
I've been charging $150 for an install.
That doesn't include fixing up templates or adding in mods, but it does include importing the 1.1x database and getting everything running in 2.0 mode. Your old links 1.1x installation will still run, and this will run next to it, until you are ready to make the change over.
I've usually been able to do it 24 hours of request.
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