Take I 80 east (I 94 ties into I 80 a few miles before the Indiana border) to I 94 east (I 80 splits away from I 94 20 or so miles into Indiana, I 80 is toll I 94 is not) to US 20. The I 94/US 20 interchange is closed due to construction on the off ramps (not sure for how long). You can use US 421 towards Michigan City and pickup US 20 there. The section of this route from where I 94 meets I 80 until the I 65 interchange is very, very, very
busy with truck traffic. Plan your timing to come through here in the early morning hours or very late at night if you don't want to be stuck in stop and go traffic. Don't go on Friday afternoon, that is when the Illinois people go to their summer homes in Michigan.
I just traveled that route on my way to Niles, Mi. on Sunday. At 7 AM I was able to do 70 MPH. On my way back at 3 PM the speed was 30 MPH most of the way.
You will only have one toll in Illinois. It is $2.75 (4axles) with an Ipass or double that amount if you pay in cash.