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
