I've been here before: I created a range of references (in the default relative format), and then I wanted to copy those cells without changing the references.
This is an easy thing to do if it's one cell. Just toggle F4 to set up the original cell just right, and then copy it.
But that doesn't work for a range because F4 only works on cells.
I was kind of surprised that there wasn't a menu option, hotkey, or function to do this. There are some solutions available online, mostly involving VBA.
Then I checked out this thread at Ozgrid. And 6 posts down, Mike Rickson notes that the equals sign used in Excel formulas can be used in Find and Replace.
So all you do is find "=", and in my case replace it with "=$", an you're good to go.