In S2 ep35 "Nora" the same opening scene was used like in this (The Jailbird) episode.
It's stated that the rifle for sale in the store is worth $300. The Rifleman takes place around the year 1885. $300 in 1885 is worth $8,402.97 in 2021.
Though filmed for the time period of the 1880's, Lucas is wearing Wrangler jeans that weren't invented until 1947.