When my father was alive, I traveled with them to do my mother's care. My dad paid my cruise and airfare, I paid the rest. My mother's live-in caregiver stayed home or went on her own vacation and we paid her usual salary while we were gone.
Now, I do all my mother's care when we travel (I don't live with her), but we did take her live-in care giver with us a couple of times. Both times we gave her the cruise as a gift (birthday or Christmas). She and I both did care for my mother, and the 3 of us shared a cabin.
We pay her a weekly rate (not hourly) so we just paid her what she normally gets during the cruise. We paid for the shore trips that she did with us...those she did on her own, she paid for. We also did not pay for her drinks or other optional extras. We paid her tips.
It really comes down to what you negotiate with the individual caregiver. If you are using agency staff, then the agency is likely to dictate what you pay.
1986 HA Constitution: Hawaii 7 day
1988 NCL Skyward: Western Caribbean 7 day
1992 Crystal Harmony: Transcanal 15 day
1994 Golden Princess: Mexican Riviera 7 day
1995 HA Independence: Hawaii 7 day
1997 Celebrity Zenith: Transcanal 15 day
1999 Grand Princess: Mediterranian 14 day
2000 Regal Princess: Alaska Inside Passage 7 day
2000 Crystal Harmony: SF to Sydney 20 day
2001 HAL Ryndam: Cape Horn/SA 17 day
2003 HAL Statendam: Hawaii RT San Diego 15 day
2003 RCI Vision of the Seas: Mexican Riviera 7 day
2004 HAL Ryndam: Sea of Cortez 10 day
2004 Island Princess: Hawaii RT LA 15 day
2005 Island Princess: Hawaii RT LA 15 day
2006 Celebrity Mercury Mexican Riviera RT San Diego 10 day
2009 Sapphire Princess Mexican Riviera RT Los Angeles 7 day
2010 Sapphire Princess Mexican Riviera RT Los Angeles 7 day
2013 HAL Westerdam Alaska Inside Passage RT Seattle 7 day