According to public gathered and assembled data from one Redditor, it looks like the maximum average per backer to Star Citizen is just under $400.
In fact, it’s about $383.55. This information was compiled through scripts fetching data from Spectrum’s APIs. As the poster notes, it shouldn’t be taken as gospel and could contain some “weirdness.” The summary of statistics include backers without Concierge (or just backers), removed accounts, the minimum Concierge contribution, subscribers, MMHC (million mile high club which include high value spenders above $10,000), and the maximum average per backer.
The max backer contribution as of this writing appears to be $253,192,024.93 with the minimum Concierge contribution coming out to $62,324,000.00. You can actually check out the searchable database here. If you’re interested in the script sources and raw database files, you can do so here.