The
craigslist ad that was just shared is a really good baseline for a deal. 5 years old, 2700 miles, $7500. When I bought mine many years ago it was 2 years old, 2900 miles, $9500. I was always extremely happy with that price. From that recent ad and others I've seen over the years, that's the range I'd be looking at.
Honestly, if my budget was $15-17k, I still wouldn't buy a new one. When you can get just a couple years old, very low miles, garage kept and in pristine condition, for over $5k off of new… I'd much rather put that $5k to accessories and mods. Sorry Triumph! There are just too many people with money to burn buying toys they don't use, eating it when they sell a couple years later. Our gain!
As for specific years, as has been mentioned, you can't go wrong with your price range. You'll be looking at models probably a few years later than 2008, so I wouldn't think twice about it.
Exciting times! I'm curious how you've managed to drive a few Rockets without owning one… very trusting friends? The used dealer I bought from wouldn't even allow a test ride. We started it up but otherwise I bought without even riding it around the block. But I sure had The Grin™ all the way home that day!