Huddleup,
What length is the barrel you have now?    If you want it real short, less than 22" you could have it cut and the bead replaced for around $50, maybe less at Gander.  If 22" is short enough for ya, then you could go to Wally World and pick up a Youth 20ga w/Mod choke for less than $100.  Many have found that a Mod choke shoots slugs as good as a cyl. bore.  It just a matter of how much $$$ you want to spend and if you want a shotgun that is really custom.  If the open sights is a big thing for you, then the Tracker I barrel from the factory is the way to go.  That's gonna end up costing you close to $80 by the time you are done.  If I remember correctly, is about $47 for the Tracker I barrel, $15 fitting, $10 shipping and then whatever it costs you to ship the receiver to H&R.  Pretty close to $80, maybe more.  You just have to decide what ya want and go from there.  Good Luck
cookiemann