We have project activities now and then where a few of the employees agreed upon at the last project activity set something up, like a bowling night, board gaming night, movie night or, for that matter, jujutsu test practice which we actually had once. The costs for these things tend to range around 10-15$ per person, 5$ more if you count food. At the moment, everyone pays their part of it every time.
I don't like this situation. Management continuously encourages us to set these kinds of things up but they don't want to contribute any money at all to it, saying that there's no budget for this at all. During the year we will get a bonus of around 2000$ since the company has been doing so well, btw.
Basically, I want to show a few of the managers how to correlate the company taking care of their developers with a considerable increase in code quality, resulting in a more efficient project and, in the end, saving multiple times what the original investment was.
I can imagine the sort of investments we'll be talking about would be getting to pick your own keyboard and mouse, your own screen configuration, desk chairs, offices, group activities, etc. What the investments actually are can be discussed later, but first there needs to be some money for it.
On to my question: I am looking for some kind of statistics, reports, blog posts (not from Joel or Jeff, already reading those) showing a correlation all the way between costs and happy, motivated developers. I don't want a discussion and mostly external resources, unless it's a very good and long answer relating to personal experience on the subject.
NOTE: I have noticed that some of these questions get closed due to non-relevance to SO and some don't, but haven't seen a clear correlation. This is, however, the best place I can think of to ask such a question, but I am aware that it may be toeing the line. Also, I don't know if this should be in the wiki since I don't know the criteria for that.
EDIT: I will close this question for now and get back to the subject once I've read Peopleware and a couple of other books. Thanks for your answers.