The whole thing, or just the head? Does it have lettering on the head, and are you worried about that staying crisp? I worked at a chrome shop, and your question could have about 20 answers. If your spotlight is a Unity or Guide, just find a really clean one and swap it out, the cost of chrome would be much more than the value of the light. We always had a hard time keeping the lettering on an Appleton spot nice and crisp unless the housing was really straight and clean to begin with. Any buffing or sanding in that area really washes it out. You need someone who is an expert to replate one of those and keep the lettering nice. One wrong move and it's ruined forever.
OK I see pictures now. The handle is a standard Unity style, that you could replace cheaply. The 3 pieces of the head (body, bezel, and base) would probably run $100-$175 each, so figure $500 in chrome all together. Also keep in mind it will need to be totally dis***embled including any rivets, so you'll have to find a good way to re***emble it. If you can find an NOS one or just a really clean one with the same head for less than that, it might be worth just replacing it. But if it's a special piece (and it looks like it might be) I think that's a reasonable estimate.
On my Appletons , the chromer took them to a jeweler who etched the lettering/numbers in deeper so they wouldn't be lost in the buffing process..
Has a mirror on it kind of hard to replace with a cheaper one that's the only one I have on the outside of the car unless I deleted and put a mirror on it