About an hour of a senior developer's fully-loaded cost.
To be clear, 8hrs/day, 40hrs/week, 50weeks/year is about 2,000 hours. Are you really saying that "senior developers" make 250USD * 2,000 = 500K USD? 250K is more like it, and only in very high cost locations -- Silicon Valley or NYC. More like 150K in rich countries, but not the richest city. Hell, 100K EUR can get you some very good developers on the European continent.
In the US, the salary is only about half the cost of an employee: the rest is taxes, cost of benefits like health care, etc.