We are also going for 10-11 days, Dec. 5-15 flying out of DTW.
Here is the best rate I have found and how I got it.
http://www.parknflynetwork.com/referrer/google/dallas-freeday.htm?gclid=COno1MHjhJACFRE_OAodBxCHvA
Sorry if this does not come up as a direct link you may have to enter it manually. This takes you to a site called the Park N' Fly network. By going to the address I posted above you get an additional free day.
Click on "get your free day, click here"
On the next page click "Locations" at the top of the page.
Click on "Detroit" on the map
next under quick quote enter your information and airport ,"DTW"
I was able to get a rate for our trip of $75, taxes included. Without going to the address I mentioned above the rate was $80. This is for the "Airlines Parking" location very close to the airport. Many of the other off airport sites had weekly specials but the extra days that we needed add up quickly.
I believe there is a $10 dollar cancellation fee if you cancel. and you must pay in avance to get this price.
I just made our reservation online at this rate. Hope this helps!