Your revised plan sounds excellent!!
You're right. KOA's are expensive and over-rated in our opinion. There are plenty of parks along your route with a pool and that's all you'd need after a day's drive. You will be getting in late on your one-day drives and by the time you set up and have dinner there won't be much time to make use of the high fees. Use RVParksReview.com for your search along the way.
Perhaps splurge a little on the Wisconsin Dells stop when you're near home but it doesn't have to be a KOA. There's lots to do at the Dells for the kids.
