I have a Johnny Stewart Digital Preymaster. This is the earlier wired unit, which is still in production. The price has come down on these. They're often on sale for $69 to $79. The drawback of this unit is that it is wired, and you are restricted to the sound cards they offer. But for the money it works and it works well. The only mod I made was to build an extension cable so I could get the speaker further out.
The FoxPro units are nice, at least the more expensive ones. And that's their drawback. Expense. The cheaper FoxPros have had too many complaints about lack of range and needing direct line of sight between transmitter and receiver to work.
Another alternative is to build your own. If you have any experience with MP3 players, this is a very viable alternative. Or you can put sounds on a CD and use a CD player. Varmint Al, at the link, has a very long webpage full of free calling sounds you can download, plus instructions on how to make an electronic caller.