If you want Ghost Ring Sights, the barrel is only half of the equation, as the actual "Ghost Ring" sits on the receiver, not the barrel. To install Ghost Ring Sights on a shotgun that does not already have them requires drilling and tapping the receiver.
Also, if you want parkerized, you are looking at the "Police Model" stuff, as the Express lineup is matte blue, and the Wingmaster lineup is gloss blue. The Police model stuff is more expensive.
Mossberg manufactures and sells 870 barrels at a cheaper price than that offered by Remington, but not in the configuration you detailed (Ghost-ring and parkerized).
What I ended up getting was an 18" Rifle-sighted, Improved Cylinder, Parkerized "Police" Remington barrel from Brownells (I replaced the factory sights with XS 24/7 Big-Dot sights).
You can also get Remington factory extensions from Brownells, but the Parkerized ones are about $90.00, blued ones are cheaper.
Tac-Star makes extensions for the 870, but the general consensus is that they are pretty cheesy! Choate and Scattergun Technologies also has them.
If you get an extension, don't forget to get a longer magazine spring, too!
The original 4-shell one is not going to function properly in a 6-shell mag tube.
Also, make sure you get a clamp. Scattergun Technologies shows pictures of their shotguns without a clamp, but I think it makes more sense to support the extension because it is in a rather exposed area if you drop the gun or bump something with it. Brownells also sells clamps.