Hello again Brett

Prefixes and suffixes are not carried over from wpDataTables into charts, the chart engines don't allow it, so you will need to use callbacks.

Please take a look at this page in our FAQ section.

It is a callback for adding a $ sign prefix to one Y column, and the % suffix for the other column, but you can use it for the X column, if you alter it a bit.

So, you can try something like this:

<script type="text/javascript">
jQuery(window).on('load',function(){
    if( typeof wpDataChartsCallbacks == 'undefined' ){ wpDataChartsCallbacks = {}; }
    wpDataChartsCallbacks[94] = function(obj){
        obj.options.xAxis[0] = {
           labels: {
             format: '$ {value}'
           }
        }        
    }
});
</script>