i'm unaware of a good, cheap, atv spreader than can spread salt. most cheap ones will either clog up a lot or rust out on you if you aren't obsessive about keeping them clean (ever try to pressure wash a piece of equipment in the icy weather? no fun...).
to resist a corrosive environment and keep the salt flowing (especially once it draws a little moisture) you need either a stainless or plastic hopper and a large agitator. large agitators take considerable force to turn when the hopper is full. thus, cheap models tend to have two failure modes: corrosion and stripped out agitator gears.
i'm sure others will chime in on things that sort of work, but i wouldn't count on a smashing performance from anything that doesn't come with a decent price tag. ;-(
amp