If these two sets of data are coming from the same data source, then the easiest is to use a multiple tables connection so that way you have one data source with all the info, I set that up in the attached. Even if they aren't from the same data source, there are a variety of techniques you can use via linked worksheets, tables, etc. to create a federated data source. I set an example up in the "multiple tables" in the attached.
Alternatively, you can add a sort by using Tableau's alphanumeric sort. I created a calculated field that returns the -SUM(Average Money spent), set it to Discrete, and put it on Columns to the left of Client. Then I made sure that the Ranking calc uses a Compute Using of Table (Across). I'm almost certain this kind of arrangement (sorting by the field from the secondary) will only work because the we're using relative addressing, i.e. Table/Pane Across/Down, I haven't been able to find any way to get it to work using fixed addressing (i.e. an Advanced Compute Using or specifying a particular dimension for the compute using).
Thank you very much Jonathan !
The best way is the multiple table, thank you !!