Developing on-call rates

I've been asked to take charge in negotiations to settle a compensatory amount for being on-call at the residential care facility i work at. We take on-call 24/7 Monday through Sunday taking turns between the nurses at our facility. Our being on-call is on top of working a regular 40hr wk. (handling staff call-ins 24/7 and resident situations during off hours) the administrator has never paid for on-call time in the past and doesn't know where to start nor do I. I was thinking a nominal amount for each day versus being paid for each off the clock hour. We're a small facility and don't handle emergency situations often, Does 25-30$/24hr sound fair? ($210/wk)

Any advice from similar circumstances would be appreciated! we're not a hospital!