At top level, the tournaments are under different organisations (ATP and WTA) with the prize money effectively depending on sponsorship. At grand slams, I would argue they generate similar enough revenue to be given equal prize money. The slams come under the ITF, and then I’m fairly sure the tournaments individually set their own prize money. All this crap people sprout about 3 v 5 sets is completely irrelevant, it’s never about the length. If that were the case, Cricketers would be the highest paid atheltes in the world.
When I used to follow tennis, I remember reading up on some of this stuff. The lower level tournies on the WTA tour would have winner’s prize money of approximately 35k IIRC, with the lowest level tournament at ATP level having a winner’s cheque of upwards of 90k. However this was years ago, couldn’t tell you what the disparity is now. It’s all sponsor and publicity related, fact is men’s tour throughout the year generates a lot more interest. Below this level, you then have ITF tournaments where both men and women earn very little (i.e. below the top 100 or so players), hence you see more match fixing than at slams etc.
Anyway, just my understanding of things.