Sorry I misunderstood you.
Ruger would probably charge you about $100 for that service. But I'd email them and ask them before buying the gun.
Another thing worth thinking about is to start shooting DA more often. Lots of folks here believe DA/SA revolvers should really be shot DA most of the time. The thought is that if it ever comes down to using it, you may not have time to cock it, and if you do, it may give the bad guy the time he needs to drill you first.
I posted a thread recently polling people and asking them if they heard a sound in the night, and were going to investigate with their revolver, would they cock it or not. The overwhelming majority voted no, and some folks even said there's no difference in accuracy or speed to get that first shot off.
I just bought and SP-101 new, so I had the choice. I went with the 3" 357 with DA/SA hammer. I figure it is good to have the option. Someone else can vouch for this, but I believe the DAO models are even smoother in DA than the DA/SA models.
In the Library of rugerforum.net (see sig), you can download IBOK (Iowegan's Book of Knowledge. Iowegan is a retired gunsmith that posts there) for the SP-101, which will tell you how to smooth up the action and replace the 14 lb. hammer spring for a 12 lb. one to make this an even better DA shooter. You have to have 10 posts before you're allowed access to their Library.