Idk. If their other option is to truck the water to an SWD you have quite a bit of leverage on pricing. Ultimately it comes down to their other options, and how much oil (revenue) they might lose if they don’t dispose of the water.
This is 8 years back, when oil was pretty much exactly this price, but it would cost us $3/bbl to truck water and we would pay < $1/bbl to dispose of water at an SWD. So for a pipe connected SWD we were paying < $1/bbl. And there was a lot of incentive not to truck water. But there were a lot of options.
In Permian. I know zero about Kansas.
How much water is it? How much of a pain is it? Is it compatible with what you are currently putting in the SWD well? What the actual heck are doing with an SWD well and asking clueless internet people like me what you should be charging? 
Good luck