>>I launched a very simple MVP (an e-blast with a mock of my product)<<
How Is a mockup a "product"??
I keep getting surprised by people who confuse Minimum Viable Product - IE something someone actually pays money for and is happy with since it does what the need it to do with "demo" or "prototype" or Proof Of Concept
MVP's have ACTUAL customers, not "potential customers"
When it comes to Google Adwords, you can usually find a coupon from Google for what comes to roughly a half month of Adwords for free. Its worth paying for them and seeing which ones lead to what response. But Adwords is actually a fairly expensive way for B2B to get traffic
Now if what you really are looking for is
>> I am specifically interested in which phrases these folks type in to Google on a regular basis.<<
Then you look at Google Trends http://www.google.com/trends/ Google Trends has been used to analyze everything from the level of racism in voting patterns during the 2008 and 2012 elections in the USA to what movies are hot