You can pick up any mouth blown distress call on the shelf and have good success. They should not cost you more than $10-$15. If you want an inexpensive electronic caller then follow these directions.
Follow the directions here
http://www.predatormastersforums.com/homemadeecaller.shtml]http://www.predatormastersforums.com/homemadeecaller.shtml
Then go to a site like Varmint Als and download some sounds.
http://www.varmintal.com/ahunt.htm]http://www.varmintal.com/ahunt.htm
I have been using his 16min sequence lately and it has been working well.
I think I have around $60 into this one.
Spend some time on Varmint Al's site in the predator section reading. He has some sound advice. Good luck