Carolina,
I was looking into the same thing about a year ago. I am a COM ASEL with about 600 hours (250 below 500 AGL, and some "Alaska Time"). From what I gathered, now is the time to get into ag flying. The old operators are getting out, and the insurance companies that drive the business are, at least, willing to talk to you these days. My advice to you would be to go and talk to a local ag pilot and find out about the business in your area. They will have an insurance agent to refer you to, and will probably even have some experience with the schools. Talk to an insurance agent BEFORE you write any checks to anyone for any training to make sure that you will meet the insurance company's requirements with the specific training program. I remember there being some specific requirements that the insurance company required, but I can't remember what they were.
I checked into it pretty thouroughly, and I think that my premium for a 300 series Air Tractor, or a Pawnee Brave was something like $11,000 a year for fertilizer/seeding/herbicide work. I think that it was herbicide, because most of the work where I was (in central IL) was fungicide/insecticide work, but it could be the other way around.
That being said, there are operators out there that will help you with things, and there are operators out there that will not. I think it would work best if you could find one that wants to sell you his business and will work you through the first year, with its insurance, applicator licensing, and flying experience difficulties.....
Anyhow, if you have any other questions, PM me, and we can chat. That's the stuff that I remember right off the top of my head right now though.....
--Matt Rogers