According to [1] there were 1,425,722 downloads of gimp-2.8.6-setup.exe from SourceForge last month.
According to [2] that file is 90.1 megabytes
So that one file used 122.5 TB of bandwidth in that month.
Assume for the purposes of argument this is 100% from the US and follows the cloudfront pricing outlined at [3], and per-request costs are trivial.
(10 terabytes) * (0.120 US$ per gigabyte)
+ (40 terabytes) * (0.080 US$ per gigabyte)
+ ((122.5-50) terabytes) * (0.060 US$ per gigabyte) in US$
= 8960 US$ [4]
So, for that single file, about US$ 9000 a month.
It gets more expensive if people download from other countries, and 22% of downloads were for different files not included in the download count for the most popular file, which I used above. It would be trivial to top $12,000 a month in cloudfront fees.