Find a local child care center that has after school care. OR use the after school care program through the kids school or the YMCA. It's pretty easy to find good child care for school age kids if you just call the centers and find out who takes that age group and goes to your school.
OR you can just sit in the parking lot of your school and see what child care centers come to pick up kids. Then call and get their prices. I would imagine it wouldn't be much over $100 per week for 3 school age kids.
A lot of places will do family discounts too. First kid is $XX then second kid is $xx and 3rd kid is $X.
A babysitter is alone with your kids in your home and there aren't any checks and balances. In a center there is always other staff around and there are always parents popping in and out. I think this situation might give you peace of mind.
I know I liked the kids going to after school care, they played games, did puzzles, kept active, watched video's, did stuff with their friends instead of coming home and sitting and vegging out.
One thing, do not let anyone else help your kids with any homework, you are responsible for that, not anyone else. You don't know their teaching style, you don't know if they flunked that topic, you don't know anything about the work they do while you're not there. So have the kids do their homework when you're there with them at home.
I made it a policy across the board that kids were not allowed to do homework at my center. Some parents got mad but I told them it was not my job to make their kids do school stuff, it was my job to supervise them and make sure they were busy doing healthy wholesome activities.