+1 hat cam-$99 at HK, very light good quality but no zoom! I agree on a viewfinder. In sun the LCD is useless. We were filming the other day and GH figured out that using the top of the swing out LCD as a cross hair worked best to track the target. For $50, not sure of the quality.
The hat mounts are only 19.99..... I was referencing the post above mine
Most cameras have a 1/4-20 female thread in the bottom for use with a tripod. Easy way to do it would be to drill a 1/4" hole in the bill of a hat, and bolt the cam to it.