I'm going to relate an anecdote (this is not my recommendation) and then I'll recommend something you might not have considered.
A random iOS dev in Calgary created an app that showed the power grid usage. He included charts (this was very early iOS days), and everyone asked what charting lib he used.... he said Excel. WTF? He actually set up a Windows server, with Excel, and hit an API endpoint, which used Excel to generate the chart and export the image, which he loaded up in his app. It was only generated daily, and there were only 3 or 4 charts. Crazy, I know. But it worked for him, and he knew how to do it.