Both are incorrect, you cannot get $0.50 to $1.20 for clicks. By the way, just you can take rough idea from these CPC but cannot expect same click rate for adsense.
Without more details being provided I might not be correct but from your description I suspect you are looking at two different things. Market Samurai shows you a figure that estimates potential earnings from the #1 spot, Google shows you the CPC charged on average to advertisers ? are you confusing the two things?
I emailed Market Samurai as to why there was a difference between Google Adwords "Average CPC" and Market Samurai's AWCPC. I got a reply from Rachael. Here is a summary of her explanation: The "average cpc" in adwords is just a baseline price that google throws out there - you still have to bid on the keyword - the final cpc might be higher or lower than the "average" baseline. So, when you hit the "Analyze Kewyords" button in Market Samurai, one of its functions is to "bid" on all those selected keyords for you. The resulting AWCPC for a keyword is their calculation of what you would pay if you had the #1 ad position for that keyword. I hope this helps to clear up some confusion As far as adsense publishing goes, remember that you only get 68%
No tool gives you a 100 % match if you do a comparison. It is because they have been built differently and take different factors into account. So basically none of the tools is wrong and none of the tools is right (Am I making sense?) Just make sure you concentrate your attention on the patterns that show up in both the tools and if they do deviate somewhere then stick with G.