This is a terrible, terrible idea. The mods of each subreddit are what keep the subreddit alive, and subreddits are the building blocks of Reddit. There are mods who put tons and tons of time maintaining the quality of their sub(s), and they are volunteers and don't get paid for any of their work. Asking them to "pony up" their own money would, with no doubt in my mind, drive them away and completely destroy Reddit. You are grossly over-estimating the number of mods who would "help foot the bill," and completely forgetting about how much hatred Reddit would get form the community if this was implemented.
If Reddit considered this strategy for monetization, they'd be much better off shooting off their foot, then shooting their other foot.
If Reddit considered this strategy for monetization, they'd be much better off shooting off their foot, then shooting their other foot.