With taxes, office space, laptops, offsites, insurance, etc a rough rule of thumb is $250k for an engineer. $250k * 3 = $750k, and over 3 years that's $2.25M (doesn't include software, hosting, lawyers, contractors, marketing, etc).

Yeah, they probably spent less than that (esp the founders salaries), but my point is that $2.2M isn't as much money as it seems.