Most big sites are paying many thousands per month. All on 24x7 support with redundant servers, load balancing, escalation plans, the ful works.
But as Colin says, that is a drop in the ocean.
Take a big site like tesco.com. They recruit for 30-40 contractors at a time, on around £45/hr = 45 * 7 * 30 = £9450 per day = £190k per month or so. OK, they might not have that many all year long (but I wouldn't be surprised if they did'n't), but they probably have more than 30 on staff at any point in time.
Certainly another big site I know of, the client pays £250k per month for maintenance and content updates etc. For the client they can just email, call or fax what they want and it gets done. Which suits them.