Rich - I found our FR at an independant local dealer on the forecourt, they specialise in VAG cars, but I don't think they realised TDI's fetch more than the petrols, hence the low price. I think the insurance for both of us is £220 fully comp and the Cupra was up near the £500 mark. A big difference if you want to start saving some money....
I would get a list of local independant dealers and search their web sites, use Google to find them.... Also have a word with your local Seat dealer, express interest in any px's that may come in and if your not bothered by having a warranty / px see if you can do a cash deal with them.... As you say, kepp your eyes peeled on Autotrader and Ebay, but be careful and get HPI checks done.
Best of luck..