I have loaded about 20,000 rounds of 12 gauge for my Bunker/Olympic Trap shooter this year. I bought 25K primers in January 2014, and I have 4 full and 1 open boxes left.
You cannot make shot cost effectively, especially quality round, treated shot. Right now lead is about 2 bucks a pound shipped. My last delivery cost $102.97 for 50 lbs.
A MEC 600 Jr is a good setup if you are only going to load a few boxes at a time. You have to pull the handle 6 times to complete 1 shell. Very time consuming. I have a MEC 9000 and after it is set up, each pull completes a shell. I can load a flat in about 30 minutes