Somehow I have the feeling that you can bend dojox’s charting module to look and feel like http://highcharts.com/ — will be for free.
Yes, it is relatively simple. To prove a point I wrote a quick-and-dirty demo available here: Tribute to Highcharts. Obviously not everything matches 100%. Go and judge for yourself.
Update: related post on dojo-dev mailing list, which explains some details of the demo.