I purchased my Diva and used it for a few cycles in 2006, but just for the sake of argument, I'll count it in last year. Spent: 32USD for the cup, and, 5USD shipping and handling. (IIRC, I went straight from the company, but I am sure there are even cheaper options out there.) I also bought one box of Insteads this summer, for $9.19.
The tampons I used to use are $4.67 a box on Drugstore.com. I used about a box and a half every period.
I get a period every four weeks like clockwork, and at 52 weeks in the year, that's 13 periods.
Also, I used to go through about a quarter of a package of overnight pads every period - that's 3.25 packages of pads a year. Pads are $6.17.
So, money I would have spent:
13 periods * $4.67(1.5) in tampons every four weeks = $91.07
$6.17(3) for pads all year = $18.51
$91.07 in tampons + $18.51in pads =$109.58
And that's not counting sales tax, but that would tack on about $5.50, or the fact that I got a surprise extra period in Europe this summer, which with the exchange rate would have cost even more.
$109.55 - ($9.19 for Insteads, and $37.00 for the Diva) = $63.39 saved even if my Diva had not paid itself back in 2006.
Since it did, by the way, total money saved in 2007? $100.39. Money far, far better spent on trivialities such as food, clothing, and a fabulous vacation. :)