You can rust blue it yourself if your the slightest bit handy and follow the process faithfully.
A handgun & small parts can be done on the stovetop burner in nothing more than a breadpan for a water boiling tank. The smallest bottle of slow rust blue soln , some 0000 steel wool to buy, but $25 should take care of that. Some wire hooks to grab ahold of the parts,,needle nose pliers, ect.
Patience & cleanliness above all else..

I'd suggest pulling the bbl to make sure old oil doesn't seep out to spoil the finish as you build it up, but many jobs are done w/o doing that.
A simple 'polishing' job for a working mans rust blue can be accomplished with nothing more than a wire wheel on the oiled surface of the steel parts.
The rust blue will matte the surface some and blend in well with that prep.

If you count your time,,it's probably not worth it, especially if you've never done things like this before.
But if you like the idea of a classic rust blue and something you can do yourself,,why not..

Hot salt bluing is what the factorys use now and is difficult & expensive for someone to do at home, especially for one project.