I believe the limit is $1000/Q or$2000/yr before paying taxes but I'd talk to your accountant. You'll be close to the amount for sure. I agree with paying a premium for PT help, especially one day a week. We also guarantee 25 hours a week and pay holidays and vacation.
I had some HS girls come 6-12 hours a week since Ds2 was born (9 months). At first they helped around the house a bit and played with DS1. Then they started taking Ds2 so I could have a break. They have been such a blessing and well worth the money ($10/hour).