I'm a nurse manager for an endoscopy ASC. I don't hire inexperienced RNs, so no comparison there; once they have what I consider "enough" experience in a hospital setting, I'll hire. A procedure-room RN, one who is working next to the GI doc who is doing the procedure (and is therefore preparing the lab specimens, cleaning the endo room, etc) is making mid-to higher-$20's. Everyone is within a few dollars of each other, but all are experienced.
Someone who is going to be strictly admissions or recovery/discharge is going to be making low-$20's. And I'm in NYS, btw.
A big difference is that the hospitals near here usually have full-time or close to it; benefits are expected. My facility offers little in the way of benefits for part-timers (typically just holiday pay, no healthcare coverage). And most of the staff is part-time or PRN...allows some of them to work in the hospitals if they want, or another ASC even.
Another big difference is that at a free-standing center, there are no nights. No weekends. No holidays (at least not the big ones!). In other words, nurses here can actually have a life
So, if you were working at my ASC, your pay would be right where it should be (assuming you're training for the procedure room, etc?).