It may be too late to save you money on this recent job; I'd like to point out something that will save you money next time around.
BUY AND INSTALL YOUR OWN R12.
You can easily obtain a 609 certification at www.epatest.com
or a number of other sites.
You pay about $20, read a 53 page book, answer 21 of 25 questions, and wahlah, you
receive a 609 card and certificate in the mail. I bought R12 recently..paid $18.00 for a can. Sams was and may still be selling 30lb. containers for approx $20 a lb. Professional mechanics buy it for this and maybe less. Knowing this, it makes me SICK when I read about people being charged 50-75 dollars a lb. for R12.