I estimate that Aero (and others who helped with the campaign) have put in at least 250 man hours to get to the stage it's in now.
The standard hourly developer fee (PHP, not game design related, which is higher) is about $40.
That's 250 x $40 = $10.000
There are about 100.000 downloads on hive for this map.
If one in 50 people donated $5, that would equal to $10.000.
Rough and hopefully correct math