Remember, the cost to the employer is roughly double the employee's salary, therefore the $250,000 per annum cost means the employee salary is $125,000 per annum. Not exactly top dollar.
I've done back-of-the-envelope estimates before and have come nowhere near that. At best, it's somewhere between 15-25% depending on employer 401(k)/etc matching, deferred comp, and office space pricing.
The worst I could find is 40% - http://web.mit.edu/e-club/hadzima/how-much-does-an-employee-... - and that uses a much different cost basis (not $125k).
Where in the world did you come up with that number?