I have a mossy 500 pursuader model (7+1) that I wanted to look into adding ghost rings similar to what are on the 590's. I realize this will probably require some gunsmithing to get them installed.

How much does a good set cost? What about the gunsmithing cost? Where can I buy a set anyway?

go to their website and check it out.  Someone correct me if I am wrong but the rear sight can be mounted to the holes already tapped into the receiver ( I got this from here and this next part too) and the front sight has to be soldered by someone who knows what they're doing.  Now you can get a 18.5 barrel with the front sight already mounted from mossberg.  It's an option under sights, stocks and etc.  But I don't know what a pursuader means so I'm not sure if that barrel will work. with that gun.  If you got the extended mag tube I don't know if the 18.5 will work right.  You could email them.  Plus it seems as though this option with the barrel is blued????  why, I don't know?

I had a set of MMC ghost rings and front sight  on a Beretta 1201FP, had a local smith install them.  I think they are great; you may want to start there.  Wilson/Scattergun Tech  makes their "Trac-Loc" ghost rings, but I thought (and still do) that the MMC's were the better, and more durable product. YMMV.  Good luck.
Mike, NY

MMC rings are the easiest to install yourself.  Just drill and tap two holes in the rear and the front clamps around the the barrel.  Most ghost rings require the front sight to be silver soldered to the barrel.

The MMC sights I purchased required the drilling and tapping of one hole only since I was able to use one of the original holes in the reciever.  Beware though, when you order this set up go ahead and order some shorter fillister head screws 8-40x1/4", vs. the 8-40x3/8" that are included.   The 3/8" ones will protrude too deeply and block the bolt.

Mossberg makes a factory ghost ring set. The ghost ring screws into existing holes. It does require silver soldering the front ramp on, though. I did my own install using the Brownells (mid temp) silver solder and a torch. I've never silver soldered in my life but after a few tries it came out ok. I then used some teflon/moly paint to make the barrel look a little happier.

You can get the factory stuff at a lot of places, but the first one that comes to mind is the much bleagered Delta Force catalog which can be found in the industry forum.

Oh yeah, its not tritium.

I am in the same boat. I ordered a Mossberg set form cheaperthandirt for 45.00.  I have the  exact same model 500 and went to a local smith today to have him silver solder the front sight on. He didnt have the right kind that would bond to a parkerized finish he just ordered some more.  I installed the rear sight no problem on my own they fit the  tapped and drilled holes.