I haven't found the cost of a good, sealed reg to be so cheap and so expensive to service that it would make economic sense. I see regs running from $200 to $1,100, the $200 being on sale for a reg I wouldn't buy. Say a mid-grade reg set and hoses runs $450. At our shop, who uses a guy I dive with to service the regs for the last 20 years, a rebuild is every two years at $25/stage plus the service kit- less than $100, unless something more needs replaced. The non-rebuild year just looks for wear and checks pressures, operation, etc. which was $10 per stage plus parts, if any.
With all that said, I have seen regs that looked like a truck on a gravel road ran over them- and yes, they are considerably more expensive to repair/rebuild.
On the other hand, Dennis has a great point. Learn to service your own regs- I will be doing it soon. I went to an intro seminar at one of the dive shows, and there is nothing that complicated if your are so minded.
Terry