We know this is good to have, but I find myself justifying it to my employer. Please pitch in on why a development team needs a build server.
This is my principal argument:
simply because you never know how the developers create their personal releases.
You also don't need to talk about build server as in "blade that costs an arm a a leg". The first build server I set up was a desktop machine that sat unplugged in a corner. It served us very well for more than 3 years.
One you have your build machine, you can start adding some features (Hudson is great) and implement everything that the other posters mentioned.
Once your build machine becomes indispensable to your organization (and everyone sees its benefits), you will be able to ask for a shiny new blade if you wish :-)