Just did a quick google and settled on the first place that came up
Ace Rent a Car they're at the airport in Indianapolis
The cost for a mini-van rents for about 400 a week (the picture shows actual vans, but i dont see pricing for it)
O'Brien Renting and Leasing
They have a custom van with video for 550 a week -- but it's got a maximum of 1000 miles.
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Where renting might smack you aroudnd is how many miles you think you'll be doing... YOu might want to map out part of your trip...
Also - UHaul, might be another option, though I can't imagine they'd be cheap for 2 + Weeks.