Chances are your route will either be:
(a) I-190 to I-90 I-90/94 to I-90 to I-80/90 or
(b) I-190 to 1-294 to I-80/294 to I-80/94 to I-80/90
I'd research tolls along that route, compare the I-PASS/EZ-PASS rates to the non-I-PASS/EZ-PASS rates, determine how much it would cost to rent a transponder from the rental car company, and see how significantly the cost of the transponder is offset by the savings on tolls. I don't trust a rental car company to not sock me with a fine for driving through a toll plaza without paying, even if I paid the toll online, plus I'm not sure if you get the I-PASS rate if you do that.