Hi there mate, and welcome (lots of people post a 'hello' thread when they join btw- usually in the George and dragon).
You've got a nice watch in mind, and would definitely be looking at an older model with a 2500 movement, which you should be able to secure in your budget. Aside from this forum, where you can access sales corner with the appropriate contribution, I'd say Watchfinder is a very good bet and very trustworthy. Ebay is a mixed bag but you can sometimes find the odd bargain- as ever, buy the seller and keep a keen eye on their feedback etc. good luck, here's a picture of mine :)