Bonus Shift Pay

[tlc2012, ADN, BSN, MSN, LPN, RN, APRN, NP]

I am looking for advice. I recently started a new position as Neurology NP at a large east-coast academic city hospital. I work with another NP and we were both hired for full-time salary (80 hours) a week M-F day shift position. My boss has asked myself and my peer NP if we would consider helping weekends (extra shift) periodically - he said about 3-6 a year between the two of us - due to under-staffing and at residents' request.We were also concerned that those 3-6 weekend day shifts may have the potential to become 6-10 shifts a year. We typically only round on 5-6 inpatients/day and would expect this number to remain consistent. He offered an extra day off but we currently have a generous PTO package. Because it was not part of our original contracts and would be in addition to it appears my boss is open to negotiations at this juncture. I wanted to propose instead of extra day off, a bonus shift pay rate. What would be a fair hourly weekend shift rate (8-10 hours) or lump rate? Someone suggested $80-100 dollars/ hour given our years of experience and current base salary. Thanks in advance!