$100 Per acre taxes are not the case around here. I've got farms in both IN and IL, both good farm ground and pay $20-30 / acre taxes.
Only places I've seen the high tax rates like mentioned are where farmers are still farming parcels of ground on town fringes, in industrial park areas, etc.
Farming is a tough business. They handle a lot of $$, have lots of expensive equipment and generally have very high net worth which is all tied up in ground and equipment, but the actual income produced by all that investment is marginal. So, yes they are pushed to try to pick up an extra dollar off every acre, any way they can.
As an avid midwestern deer hunter, I saw how the habitat was getting wiped out years ago and realized that the only way to assure long term quality hunting was to buy ground and develop it for such. Just so happens, it's been a really good long term investment too, appreciating considerably in value while spitting out a little income each year.