Well, I have two friends, a mom and her son who do pet sitting and they charge $40 per day.
Son lives in Portland, Oregon and is a trained Vet Tech. His mom lives in Eugene, Oregon and is "an experienced mom."
So, for a neighbor youth, I think your price is about right -- at five days for $200 that works out to around $40 a day and at seven days thats around $28 per day.
Seriously, I hate to go cheap on this stuff, because it is a neighbor kid, so you want to treat them well. And, you want them to be excited about it and do a good job, so a little extra $$$ can help keep them motivated.
I sure would not want to go much below the $28 figure. Some 8 years ago or so, my daughter did this for neighbors and got about $15 per day, but that was only for a quick "let out of the house in the morning" and a walk in the evening. And it was only one dog.
Can both critters be SAFELY walked at the same time. If not, that really makes a difference.