There are many inexpensive ways to find tutoring for your granddaughter. One up-and-coming method is with online tutoring. Sites such as this one, instaedu, and tutor.com all allow you to find tutors from the comfort of home. Some of these sites even allow you to find/sort tutors by price, and find one for a price that works for you. An even less expensive (free) method is by utilizing sites such as Khan Academy or even Youtube to find videos on topics that your granddaughter needs tutoring in. This type of "tutoring" is only one way, of course, but you'd be surprised at how many online, educational videos can answer the exact question you may be looking for.
Another inexpensive method is simply through networking. I'm sure that many teachers at your granddaughter's school would be more than happy to take time after school to tutor your granddaughter for free. You could also offer to pay teachers for their extra time, but I'm sure many teachers wouldn't mind spending an extra 30-60 minutes after school to help out a student.
Finally, you could always look to family and friends in helping out your granddaughter. Maybe your granddaughter has an uncle, sibling, or cousin that would be able to spend some time on the weekends to tutor your granddaughter for free. Finding a good tutor can be an expensive venture, but it doesn't always have to be. There are many out there that love teaching and wouldn't mind doing it for no cost. Best of luck to your granddaughter and good luck finding a tutor!