We never did any study to determine how much money we had saved, but let's look at the result of our open data Apps4Ottawa contest. The initial investment was $50,000. That's it. Out of that contest, we received over 100 applications, either for smartphones or for websites, etc. After the first review, about 80 of them are what I would call of high enough quality to be considered for the contest.
Getting 80 applications for an investment of $50,000...? There's no way you could get even one developed for that cost. So we may not have savings, but we sure have a nice return on our investment.