dont know whats out of your range, but there atlantic towers "tower in a box" which is around 1500,,, and a custom built arch from pipe dreams was quoted at 1500 for reel time installed....
couple leads for ya if any thing
for the folding mast, why weld. use an alum pipe with a pivot bracket and clamp the radars plate to the top, they gotta have a mast bracket, you see'em on sailboats all the time.
try hitting up some local welding shops see what they can do for ya over a specialized place.
and another option is the guy at lakeside welding,,,, does cooler racks out of his shed part time to try and make ends meet... very good product. made the step pops rack how he wanted it, custom mounting. and had him do some welding on another rack for me that wasn't even his.
35 Sepulga Dr
Browns Mills, NJ 08015
(609) 893-6695 <--- his house number
Jerry is his name, a really nice guy to deal with, and told me if it can be done, he'd give it a shot, and very reasonable to.
found a post i did awhile ago about him, here
lakeside welding