Hard to tell what you get for volume out of the amp in that vid. There are a lot of amps available on E-bay and Amazon that are dirt cheap and powerful enough to to make good e-callers. You do need to be able to hear it across a 1/4 section of land, capability for trying to pull traffic birds may help some days as well, snows don't always cooperate on flying back to the previous spot they were in. Another thing that is nice, is being able to use a flash drive or an SD card in it, there are a number of amps out there that have that capability and can drive 4 speakers, along with remote controls. You can also use an emergency lighting battery instead of the AA packs.
I have to build another one for this year, ordered a Pyle plmr19w and 4 phsp5 Pyle horns, run that off a emerg light battery with the whole thing mounted into a double deep pistol case. I had one setup with the Pyle amp before, it puts out nice volume when needed, just put plugs in the box for jacks for the speakers.
We've used some similar to this one, worked well for 6 yrs now;
http://www.ebay.ca/itm/50WX2-Mini-Di...IAAOSw34FVHA7D
Put a couple of your dekes outside for a couple of weeks and let the wind and weather do its thing to it, to test your peg connections, that will prove them out for you.