I've contacted a few places. Roughly $80 for CNC cut 1/4" ABS for a 1 off. Shapways will print and ship on demand and they're running around the same price when shipping is added. I'm not worried about the quality of the printed plastic. I've have other items printed by Shapways in the past and that plastic is pretty tough.
I have one CNC cut (fuse) and one printed (reset) on their way along with the Blue Sea push button resets and AGC/MDL fuse holders. When I get them in hand, compare them, and make sure everything fits I'll go from there. I'm leaning toward Shapways. CNC cut would be cheaper to mass produce but then I'd have to deal with storing and shipping them myself. I'd also have to pay for it up front and hope I sell enough to cover the cost of making them.