It really depends on what you're spraying, what equipment you're spraying it with, where, your experience, and how much work is available.
I've made fifteen thousand in a season, and I've made more...and even less. You're going to be paid a lot more to fly an AT-802 vs. an A-188, you'll get more work done, and have more options. However, those seats are certainly not entry level seats. If you're doing forestry work, the pay isn't nearly so good, but hopefully you fly enough (you do) to partially make up for it...you just do a lot more work to make a living. Firefighting pays better, but like spray work, you have no idea how much you'll fly or how much you'll be making. Right of way work (spraying highways and roads) or urban insect work doesn't pay nearly as well, is speciality work in some cases, and is inconsistant. Range land spraying pays a little better, but is often parcelled out in big lots, and you'll get the tail end when you're new...and doesn't pay like row crops. Reseeding (such as after fires) doesn't pay all that well, but there are large acerages, and limited amounts of work.
As for there being a future in ag work because people need to eat...not so. People can eat without spraying, though the productivity won't be the same...and crop treatment is done by many more ways that just aircraft, such as chemigation and ground rigs.