Coming from a ranching/farming family myself, and pesting around family feedlots/etc. with airguns myself, you are not going to find a farmer/rancher willing to pay you $5.00 per bird. I can go spend less than an hour and drop 50 birds (Euro/starling/pigeon). Now multiply that by even an 8hr day, by a 5 day week (bankers hours of course), by 20 work days in a month by........ That's a lot of money! The sheer amount of birds that hang around feedlots is astronomical, and the ranchers understand that. I had a talk with my uncle when I first started whacking "pests" about invasive species, no hunting limits, etc. The conversation kept circling back to how they're not supposed to be here and he responded with something to the effect of, "there's so many that you could kill em all day every day and they'd just keep coming." In addition, the profit margins in the agriculture business are too small to make sense of paying someone to kill birds on a per/head basis. The profit margins in the agriculture business are too small to make sense to pay someone to kill birds at all, much less on a per head basis.
You're going to have much better luck finding someone willing to pay you to kill birds that has a couple nesting pairs of starlings in the hollows of a big tree they park under, or a squirrel going in and out of their attic, or chipmunks in their garden, etc. The scenario here is one specific problem critter (call him Joe the squirrel) not the thousands of his relatives that live in the wood lot behind the house of the attic that Joe likes to go in and chew on the wires of. I use that as a comparison to the rancher. There is no one problem bird causing problems for the rancher that he would gladly pay $5.00 bucks to have disappear. There are hundreds of thousands of problem birds. We're talking homeopathy here. One drop (or bird) in an ocean of birds. We're talking about removing 0.00000000000000001% of the collective army of grain eating birds. Oh well I'll get a bunch of birds you say, well say you get 50/hr/8hr day. Congratulations, you removed 0.000000000000004% of the collective army of grain eating birds (no I didn't count the zeros so don't bother fact-checking my math, just illustrating my point here). Simply not worth it to a farmer to pay someone to do that.
In regards to "pest control," I decided that my biggest motivator for whacking birds/ground squirrels/prairie dogs is just cuz it's fun to do. Yeah, yeah, I've heard all the justification of how much of a favor we are doing for ranchers/farmers but until you've sat at a feedlot and watched the birds come in, waves after waves after waves, you don't realize that it would take armies of guys with shotguns at ten foot intervals surrounding the entire place with unlimited boxes of shells standing watch from daylight to dark to even begin to put a dent in them. And once that pesting militia started to make any kind of impact in the bird numbers, the remaining 90% of the birds would learn to simply steer clear of the shotgun militia at farmer joe's (not related to the attic-squirrel).
In conclusion, I'm sure you can get some permissions where they won't mind you coming and popping whatever critters are legal to do so. You may even be helping, a little. You'll have a blast shooting pests and you'll become much more accurate/know your gun better/etc. But, the best way to get a farmer/rancher to tell you no thanks, is if you start off with the benevolent offer of shooting birds, for the low, low price of $5.00 each. (you could always try the $4.99 trick the infomercial people do, or maybe an "introductory offer" of 2 for $4.99-but only if you act now-carcass removal fee extra).
Hopefully you wont take this as a rant, but rather a humorous attempt at helping you see it from the farmer/ranchers perspective.
