I would love to know what your numbers were from you testing, thanks to this guide I decided to save up and do a test run for myself. Since Coke seems to stay between 9 and 10k I decided to try the summoning bells. I only payed for the Scheelite and the Petrified logs since I am able to farm the rest easily at this point. I payed a little less than 25k overall per summoning bell and I mass produced (thanks to netflix and macros) 100 summoning bells on saturday. I am at 100 bsm before i began and these were my results

32 Botchs
18 Fieldcraft 3 Demimateria
06 Clear 3 Demimateria

The rest were a mix of wolfram ingots ancient lumber and my favorite the feather.

By my math I could only get 28 darksteel ingot at the almost same cost as the 100 summoning bells and at this time I would be surprised if I got same or higher result out of 28 weapon parts made from the the darksteel ingots. This guide I would say has saved me alot of gil pain, thank you!