I've gone through this several times with replating small industrial parts. The reason they're quoting so high is because they're giving them the same quality finish as a classic car job. There are companies that specialize in industrial plating, but they tend to deal more with applications that require consistent finish (medical, lab, etc.), not necessarily "pretty" but sometimes more challenging to do so the price is still up there.
What we've done is go for the hole-in-the-wall plating shops. Not for lack of quality, but you need to be able to talk to someone who's hands are on the work, not just one that takes orders, and explain that you want very little, if ANY, polishing and finishing done. You can also ask them to strip the parts and send them back to you to polish, then you'll send them back for plating.
We used to work with a local company that made wire goods and had a plating department. We occasionally had some really crummy work done, but they were dirt cheap and 99% of the stuff came out perfect for our needs. Ultimately they stopped taking in outside jobs though, so now we're working with an automotive chrome shop in North Houston. Not as cheap, but better quality.
Most of the parts we've done didn't really need "polishing" so much as a buff with a wire wheel. IMO unless you are making a show finish machine that you don't ever plan on using, "classic car" quality plated items will be a waste and will probably stick out like a sore thumb against a comparatively rough paint job and bare metal surfaces polished to different degree's.
(I'm also going through this process with my 54' Chevy sedan right now. Hoping to pick up a bumper this afternoon
).
The plating doesn't really fill anything on its own, it just adds a layer, so whatever level of shine you give the parts initially will be what carries through to the plating. The way they fill in pits on car parts is to plate in copper, polish down to metal, plate in copper, polish, etc. etc. Many many coats and polishing later, the pits are full of copper and you have a copper plated part ready for nickle/chrome.