Rust blue it. That you can do yourself right on the stove top. Nothing more than a simple bread pan for a 'tank' for pistols like this. I've been doing them that way for years.
If you bead blast the surfaces first,,it'll take the blue even better.
Mark Lee's soln works well for a hot rust blue. Laurel Mtn for a cold rust finish. There are others.

or,,have it Parkerized. Another untility finish that looks good and wears well. It too gets a bead blast first generally.

Trying to stay away from expensive polishing.

I don't care for the paint/gun-coat type finishes. But you may like them and consider one as an option. Especially if the gun is to be no more than a utility piece and expected to get it's share of wear and marks in the future.
Though some are better than others,,Only maintanance and care can prevent future rust,,no matter what the finish applied.