J.J.
Try craigslist. I have had success in the past.
Our family is looking to get away for a few days over MEA weekend (late October weekend school break in MN). We'd like to stay at a cabin within a few hours of Minneapolis, preferably on a lake. Our daughters are 7 and 1. My hubby's mom will be with us for sure and potentially his brother and his brother's girlfriend, and we all enjoy outdoor stuff like fishing and hiking and campfires. Our budget is less than $200/night for lodging. I have been looking at cabins on websites like homeaway.com and vrbo.com, but those don't necessarily show the resorts in an area. We're considering the Wisconsin Dells area, but not so keen on doing just waterpark stuff the whole time -- are there other activities nearby? What other places does your family love to go?
Try craigslist. I have had success in the past.
My family had a great time spending a day in Duluth over the Labor Day weekend. The new alpine coaster at Spirit Mountain is a lot of fun, although your littlest one is too young for it. Kids need to be 3 to ride with a parent. There is great hiking in the area (I've heard Jay Cooke State Park is good for that) and Canal Park is great for hanging out, feeding the birds, etc. We also enjoyed the Great Lakes Aquarium and it has interactive exhibits appropriate for both of your kids. I don't know about renting cabins nearby, but there are many different types of lodging available in the Duluth area. Have fun wherever you go.
the Brainerd/Park Rapids area is nice this time of year- They are winding down from the summer tourists times. Check the websites to see what is available in that area. I will be visiting Family during that weekend in that area. Good luck!!!!!!!!!!