I'm not sure you will find any rafting within your parameters.
The closest thing I know for rafting is the East Race, in South Bend, Indiana.
They rent rafts and inflatable kayaks for runs down a less than a half mile
cement ditch in the heart of downtown. (This is beyond your 'ideal' distance.)
Info at http://www.sbpark.org/parks/erace.htm

Otherwise, my recommendation would be to look into a couple rivers in Ohio,
where there are canoe/kayak outfitters which run a couple mild whitewater
rivers. I think the closest (within your travel parameters) are the Sandusky
and the Maumee, and (stretching a tad further) the Mohican. Check outfitters
info at:
http://www.ohiotourism.com/discover/...e/canoeing.asp
http://www.oweb.com/Advertiser-Tribu...acesToSee.html

Much may depend upon the age(s) and height(s) of your group. Some outfitters
may have requirements regarding either. Good luck!