Make cactus green dye $0.60. This would not mess with the economy, as people who buy /smelt will normally not risk a ban for auto farming.
First off, it would not be that suspicious because the mining world is always full of cactus (I got like 4 inventory's full of them), and second off, once cacti became more common, they made them worthless (used to be $2.50 each) due to the fact that someone can try to bypass the cactus farming roadblock. Having green dye have worth is just like selling cactus to the server, just with extra steps.
OK, middle of mworld, nearly all cacti gone, some guy comes along with 25k worth of cacti. What happens then?
It's called supply and demand - things that cant be found easily (like near end of the month) can be purchased from other players, or from the market, or from the colourshop. Personally as someone who uses a lot of dye for banners, it's not that hard to manage.
Would be a good idea, but would probably drive a good bit of inflation. Eh, would be a good fix if the SA's only did it if there was a lotta money taken out the economy, like really big amounts of lotto pots or a major business collapse ;-).