In a world of so many wonderful free open source graphing libraries, it's hard to see any reasonable licensing option for this. It might help if there was a page that listed features that a developer could not accomplish for $300 in flot, highcharts, or ndv3, or other popular options.
Highcharts is cheaper if you use it for a single webpage (90$) but if you want to use if for a real web app it's more expensive (590$ for a single developer).
Having said that, in my enterprise my dev colleagues use it and they think it's a great product.
EDIT: if you host it for a personal/non-profit project it is free according to Creative Commons Attribution-NonCommercial License
another product we've used in the past is Amcharts, good buy maybe not good as Highcharts
