The rate range is huge, and it all depends on what is offered. The last time I checked about 7 years ago, around here, centers are around $200/wk for infants, and around $160 for older children. In-home is anywhere from $85-$160/wk, depending on age, area, and how much is being offered (licensed, nutrition program, preschool, etc.). I offer all of it under the sun, and charge $135 for babies, and $115 for older kids.
I would suggest for you to increase now by $15 per week. That is not a lot of money, but will add up nice for you. Two-weeks notice is plenty. Just a short note of the change is all that is necessary. Your DCFs know the freaking awesome deal they've been getting, and won't be surprised. Then, I would up it again in January to where you want it, with a chart that compares your rates and what you offer with everyone else. With 2-weeks notice again. You don't want to give them too much time to shop around.
When I did my rate increase, that's what I did. It took some sleuthing, but it was worth it, and no one could argue that they were still getting the best deal around.