Well, not sure the logistics/cost of sending it to ID..?
1 gallon neem should make 200-250 gallons mix.
To drench completely 50 medium size plants I use 4 gallons mix no problem. I'm very liberal with my spray and err on the heavy side. But when I'm done no soft bodied sucking insect is alive. Keep in mind neem is not a 1 time spray. So, you said your pepper patch is 4000 plants..? that would take approximately 2 gallons of pure cold pressed neem for every spray, if my math is correct.
As with most organic less harsh methods, after initial knock down, a constant preventative spray every 7-14 days will be needed. @ $50-75 per gallon neem oil cold pressed, each spray will cost you $100-150 and probably a full night to spray, putting down close to 400 gallons mix on your 1.25 acre pepper patch.
If you are having a current infestation of Aphids, here is something you could do immediately with whats on hand locally. You probably already know how to make it, but I'll give you what I use to do before using neem, and it worked pretty good. Not as good as neem for any lasting repellent type properties, but it did the job very inexpensively.
A simple home made insecticidal soap. 1 gallon water to 2.5 tablespoons mild soap mixed with 2.5 tablespoons vegetable oil, or peanut, or corn, or soybean oil. Add 1tbs cider vinegar if powdery mildew is also a problem. Some recipes call for 5tbs soap/1 cup of oil but that much is not needed imo. You must keep it mixed/shaken vigorously. Keep shaking your sprayer constantly. If your water is hard use distilled water as hard water will make your insecticidal soap much less effective...Keep sprayer pumped up to max pressure. For this to work you need a strong spray that drenches undersides of leaves/tops/stems and gets into every nook and cranny....
