Welcome :)
Firstly I would save up and get the one you want because anything else is not it.
Secondly if you are considering buying from the US you need to factor in the shipping and potential import charges that could eat up some if not all of that 100 pound saving.
For me I would buy in the UK as if anything goes wrong its easier to sort out.
Try a WTB when you have 25 posts, I have never heard of authenticwatches.com but that doesnt mean they are not good :)