the tone of your last sentence is not really in the spirit of the forum, two of us have tried to answer the question you asked with the views which we have, it is not a case of not being able to afford a boot fitter, the majority of general ski stores who have a fitter on staff do not charge extra, how much is too much........ if he spends $150-$200 on a boot for a couple of seasons back which is not close to being right then that is money down the drain, it will (or certainly could) cause him a lot of discomfort, pain or possibly injury.
I can certainly answer part of your original question but you will not want to hear what i am going to say... The dragon 120 is based on the dragon 120..the dragon last was a new last fron Tecnica, it replaced the diablo range but is a different shape, width, volume instep height etc etc.
you summed up the problem really nicely when you said
His last boots were the Nordica GTS 8 and found them uncomfortable and painful. Happens when you buy from sportchek. He wants a stiffer boot, so around 100+ Flex
doing what you are proposing is no different.
if he wants to get it close as possible without the expense then he should read as much information in the wikis as he can, understand shell fitting, and how a boot should feel then start trying them on it will always be a gamble but the more information he has the less of a gamble it will be