Do you read classics?
Instead of paying for them, you get them free. Enough to spend the rest of your life reading for free.
Do you like SF/Fantasy?
The Baen Free Library and Fifth Imperium CDs might justify the cost.
Like romances? Harlequin and other promotional freebies might do the job.
The thing is, ebook readers are *not* about saving money on content. They're about a better reading experience. You *can* make an economic case for them but it rather misses the point; it's like saying TVs are about watching movies for free. Which it can be, but...
And if you're looking for anecdotal info about post reader-purchase buying habits you are in the wrong place.
Most people around here are avid readers who will merely testify that, yes, they're buying *more* books than before.
So if you want to make the case that a reader will save you money, you can.
But odds are it *won't*.
Few are that strong-willed.
Good luck!