Something toi consider-those chickens are shot up with all kinds of MSG, phosphates, tenderizers,butter/margarine, etc before they are cooked-that's why the taste so good. Therefore the protein assimilation will be substantially reduced and the caloric content increased. Think of it like eating a piece of steak vs eating a similar amount of beef jerky. The steak's digestibility and protein efficiency would be much better than the beef jerky cuz of the chemicals.
You didn't do bad. Personally I like to find out what time the deli closes at my grocery store and I go in right before they take the hot chickens in back to the fridge(usually they're chopperd up the next day and sold in ready made chicken burros or on top of pre made chicken caeser salads). A lot of times they'll sell them to me for 1/2 off. Last time I bought 3 of them for $9. I ate 2 of them over a 6 hour period (with a couple salads)and put one in my fridge for the next day. I can assure you of one thing. Eating 2 of those chickens for $6 was a much better investment nutritionally/cash-wise than ordering 2 double 1/4 pounders w/ cheese-which costs around the same.