I'm looking for Sun Protection as I live in the lowland Tropics only 400 miles from the Equator. I already wear a black, lightweight UV Buff neck-tube around my neck, but it never quite stays down to fill the gap to the collar of whatever cycling jersey, and I'm left with an inch of exposure.

I'd rather not cake on the sunblock down my neck. (Sunblock is $25 a small bottle here, and it ruins jerseys and baselayers even black ones.)

Any ideas? Manufacturers?