Thanks for the replies so far. I'm still going to go down the path of building a variant of the DIY caller on the predator masters web site. I already had the MP3 player, so the remainder of the items will not be too costly. I'm still "shopping" for a camcorder wireless mic. I would like those units to run off of 9V batteries, so I can incorporate 9V RC Toy car rechargable batteries. Seems to me this would be the best way to go as far was power. I looked at the Azden WLX Pro, but not 9V, still looking for NADY 351, or Azden WMS pro ... either runs on 9V batteries and seems to test well out to 90-100 yards.
Keep the info coming. If anyone out there has built an E-caller, especially with wireless capabilities, I would love to hear about your setup and cost.
PASlugger.