If you're going to take more than the recommended time to get to a source of antivenin, you might as well just fly to a hospital in Mexico. The cost of the identical antivenin there is about $100/vial, vs. $8,000 - $40,000/vial in the U.S. The number of vials required for treatment varies with the amount of venom injected. The most likely possibility is that you'll have a mild to moderate reaction and won't need antivenin, but U.S. treatment could cost enough to ruin your life.