Learn to squeek with your mouth and your hand! Works a treat when you master it. And as long as you have hands and lips, you have a fox call!!
If you cant do it, or you want something in your mouth so you have your hands free, then get a widgeon whistle, and imitate a rabbit in distress with it. There is also a slightly larger one, made of brass, which will go round your neck, quite handy at times.
Both of these are cheep, and will last years and years. I still prefer squeeking them in manually though.