Hello,
Please notice that you didn't provide any details about the previous and the target Joomla version, and without this information, it's really hard to make a proper bid :) (migration from 1.x/2.x to 3.x is really not the same as upgrading from older to current 3.x.
Anyway, may help you with both.
Looking forward to hearing from you (send me a message even when I'm offline),
Adam