Interesting, I had the same problem a couple of years back on my 09 and couldn't find the part anywhere other than the dealer as well and was just as shocked at the price for this part at the local Chevy dealer although the price was a bit cheaper than the $250 they quoted you. I paid about $180 for it (which is still a ridiculous amount for a rubber tube) but it was still cheaper than the price given to you. This is at a dealer in a small Indiana town mind you so it's interesting that it is more now, I would imagine that prices would drop instead of go up as time goes on. Looks like the eBay link is the best option for you at this point. I am currently in the process of cleaning the throttle body itself and it is not an easy task for novice! Good luck on your repair!