First if the subsidies are halted many acres of land would go out of production in the basic crops we depend on. Corn, wheat, soybeans are the biggies. The subsidy generally covers the average costs of production, the elevator price is profit. (not always as any hike in a production cost can easily overlap the subsidy check, the biggest is oil, it is fuel for both production and hauling but a big factor in the cost of fertilizer and boy howdy we use the crap out of that, next are pest/herbicides)
Now the posted price is rarely what a farmer gets because that price is for the mythical perfect bushel- shriveled kernels count against the price along with any weed seed/parts found in the sample.
So a lot of the marginal land would come out of production as without a guarantee of at least your seed money back fewer farmer are willing to risk the costs. Prices WILL NOT, I say again all after prices WILL NOT fall but rather rise dramatically because fewer acres in production will drive the commodity (better named speculative market) higher.
The basic principle of farm/crop subsidies is beneficial, over the years it has been corrupted by lobbyists farmers. The purpose was to guarantee a certain POTENTIAL level of production so that drought, early or late freezes, heavy rains that delay planting or ruin some areas right at harvest- nothing worse than a late may heavy hail storm in the wheat belt, the crop gets beaten down and lost JUST days away from harvest- would not cause famine or drive the price of food too high for lower income folks. (we used to have periodic shortages as bad weather or speculative runs in both crops- tobacco in early days, cotton later- and the market drove food costs above what many could afford)
To receive the subsidy the farmer or corporation must register the acreage, meet certain guidelines and annually report the numbers of acres planted to whatever crop. This way the USDA and speculators have a handle on what potential production can be. Weather and input prices get factored in for production purposes but what subsidy the farmer receive is mostly set in stone- sometimes a supplemental payment is made in the case of extreme drought or heavy spring rains but the procedure to approve such a payment can make you take up drinking.
Anyway the free market can't create a surplus in production to insure enough food in the case of drought or untimely rains. Some sort of mechanism to insure a surplus so droughts and input cost spikes don't create food shortages is required in a modern society. Regulating the manipulation of the system for speculative profit is required.
There are so many places in the food production system where reform would be helpful, perhaps capping the total amount any one corporation/farmer can receive each crop cycle would be helpful- though the dodge is to simply create more, smaller corporation 'farmers'. Limiting the swings and capping trade in the commodity market may help.
Throwing the baby out with the bath water when it comes to subsidies would be very interesting, but I don't think many 'libertarians' would appreciate the results...