
Do a bit of shopping around different butchers. Not all of them can get chicken carcasses etc. and some are cheaper than others. (You will probably find legs are too small for him soon, especially as he gets more keen.) We use one butcher for hearts, liver and lamb bones etc. just had 12kg of hearts for £12 from him. And another butcher for the carcasses because he is one of the only ones that can get it from their processor. Fresh tripe is usually best found at an abbatoir, but I must admit I prefer to by the frozen chunks. I'd suggest sticking to chicken for a week before introducing new foods.
http://www.krisannriorawfeeding.com/pashasfooddiary.htm You might find that useful. I know your pup is alot older, but it'll give you some ideas about changing. It certainly helped me changing my adults over. Have an explore around the site. Good Luck