I got mine at Autozone, an auto parts/accessories chain store that is quite well represented locally.
Can't remember the price, but doubt I would have paid much over $40. These were round ones that replaced the rusty original round ones almost perfectly. I had to spend a couple of minutes with a rat tail bastard file on each hole to get the new ones to fit. (Better the original hole was too small, than too large.)
I never had a bulb burn out on the originals, or any malfunction for that matter, however the frames were a constant source of irritation as they rusted, and the yellow run off stained the gel coat.
This replacement was part of a complete exterior renovation
I did this summer.