At some point in the decision process you should be weighing the cost of buying software/support vs. the cost of developing it in-house. Highcharts is not expensive compared to developing something similar yourself, unless you have the luxury of a loose schedule and are being paid at something like $10 an hour.

I think the reason these "cost concerns" are being expressed is that a programmer isn't trained to weigh these things objectively. It's like going directly to a surgeon with an ailment and asking their recommended course of action. Their expertise is surgery, so their resolution is more likely to involve a knife.