How much should I be paying for in home respite care?

My mom is now at a point that she cannot be left home alone. I am the sole caregiver, so have been looking for an in home respite source. I just need to be able to go to the store and doctors appointments without worrying.
Question is, what is a "normal" rate for this service? I imagine it varies state to state. I am in CA.
I have spoken to one company. They charge $23.95 per hour, with a four hour minimum. At that rate, I really can only afford once a week, and that is a stretch.
Thank you for your responses. :)