You need to be careful: since you're obviously aware of the patent, if you were found to infringe, the patentee might (and probably could) pursue enhanced damages on the basis of willfulness. I.e., you can't claim you didn't know about it.
It is true damages are hard to prove, but they are also hard to disprove. If it comes to it, the other side will hire an expert witness to prove you owe a lot. You will thus be forced to hire an expert wit to refute, at around $300-500/hr.
Much great advice above, though some inaccurate. Best advice: it's a minefield, so don't be penny-wise, pound-foolish. Hire a good patent attorney. Not a prosecution attorney but a litigator who's experienced in crafting licensing deals. Not just a good trial lawyer but someone who's strategically savvy at keeping you out of the courtroom.