Honestly, I can't say for sure. I thought there were both appearance fees and prize money but I can't find info on either through an initial perusal of the site. I did find mention that the top 10 are determined by gun time, age group awards are determined by chip time. However, no mention of what the top 10 get. Just that age group awards are certificates.
My take on Chicago and Milwaukee is that the comparison of local runners is about what one would expect given population differences, though Wisconsin Runner probably ensures a few more regional caliber runners around the Milwaukee area. Where Chicago has the advantage in races is in drawing out of town competition. Milwaukee doesn't really have races that draw out of town competition other than Lakefront. Chicago does have some races that draw that competition and that's largely due to what those races offer.
Unless the top dog gets alot, I don't think that prize money is much. I want to say one year Carol got 3rd and it was $150-200. I've placed 8th and 9th, or 9th and 10th and it was $50 each year. The $$ is the appearance fee. I mean there is a reason that Frank S showed up and didn't run and that Uta shows and runs at a snails pace (well, for her anyway). Top 20 f/m get free entry and hotel the next year. Rumor has it, new RD. Things could change.