I am going to order a Baikal MP-18 Youth with 24" barrel for $135 from Bud's. I am going to have William at Sumtoy thread it ($35) and buy one of his chokes ($65) and have him install a Burris FF 3 336 base ($).
I also have an old Savage 949 C that has a 22" barrel. I hope to have the same treatment done to it.
In my opinion the best single shot 20 gauge that you can buy new is the TC Encore, but if I am going to spend that I would buy the Franchi Affinity auto.
Good luck!