I-35 in Oklahoma is not a toll road. Neither is I-40, the main east to west. The Oklahoma toll roads are routed as I-44 (roads were bulit before Interstate system and Feds chose to route on them) or else they are not part of Interstate (e.g. Muskogee and Indian Nations turnpikes).
I don't know about other states, but for every turnpike in Oklahoma there is an alternative route on two-lane state highways or U.S. numbered highways, going through the same population centers, and other routes going through different places, avoiding the two population centers. Often, on the parallel routes to the toll roads, travel time doubles, so I have to decide whether I'm in enough of a hurry to pay $2-3 to cut a 3-hour drive down to 90 minutes.
I don't know of a "avoiding toll roads in Oklahoma" web site, the alternatives are pretty easy to find on the state higway map.
Avoiding tolls in Kansas is trickier, because much of the Kansas Turnpike cuts diagonally across an area where the was not one single old route. But north to south through Kansas, US-77 will keep you off the toll section of I-35 south from Wichita. Going through towns, some of the speed limits will be as low as 20 MPH and will be strictly enforced.