I think $250 is steep for any brifters, but the current 10 speed Ultegras run for $400 or so, which makes $250 seem pretty reasonable.
The thing I would caution you about is that Shimano brifters are not serviceable, so if they wear out, you need to buy another pair. In my mind, this makes $250 a no-brainer, since people will always claim that their 3 or 4 year old Ultegras were only ridden for 200 miles to get you to spend your $150... They might be telling the truth, but if so there are a lot of people out there riding their $400 Ultegras for a few miles then spending $300 ($450 for DA minus $150 recovery on Ultegra) to upgrade to Dura-Ace... even though almost anyone who has ridden both claims the difference between the two is negligible.
I strongly suspect that many people selling their used Ultegras are selling them right before they expect to start degrading performance due to age while they still have some value, to support their upgrade.