I am sorry for your loss....
I have paid $400 for a 2 night 3 day trip BUT that was the sitter coming to my house and also house/pet sitting.. getting daughter to and from school, etc.
I think for a weekend and a 21yr old that your price range (CASH) sounds reasonable. My daughter would do that.
It depends on your area, I am in the far north Dallas area and the going rate for a sitter is about $12+ per hour. My daughter sits every Sat night for a family with 1 well behaved 4 yr old from 6:30-about midnight and she gets $85 regularly. Needless to say, she foregoes her date night for this job!!
Not all pay that well but the 3 she sits for regularly do. Granted, she is CPR trained, she teaches the children Spanish, she does mani'pedis for the little girls and she is well loved.
Enjoy your weekend!