Not to be too much of a downer, but your entire company revolves around the licensing decisions of a single 3rd party provider? Not sure what you are trying to accomplish by a lawsuit, but your business is over, and here is why: Option A) You give up on the lawsuit and get bullied out of the market by the sole provider. Option B) You win the lawsuit, but piss off the sole provider in the process. It's not going to be long before they make things tough on you in other ways.

Bottom line is, you put all your eggs in one basket, and someone took your basket. The lesson to be learned here isn't how to get your basket back, it's to not put your self in that situation again

Sorry to hear this, must be very hard after 9 months of hard work. If they are the sole providers of this data, a great business may be to compete head-to-head if you can start becoming a provider of this data. That may be good use of your time (not that the legal action isn't).

If they are willing to fight to the end, couldn't it take years (assuming you don't run out of money halfway/lose)? Would winning still help you any in that case?

What kind of data ?

Pricing

You can always turn this into little guy vs Goliath in the media, get free PR and crowdsource the data.