I think that the lowest price for either new (some shops appear to sell their excess inventory on eBay) or used (in addition to individuals, sometimes the seller is a shop that has 'pulled' a component from a trade-in or floor model) will probably be through eBay (US).
The exchange rate for Sterling may continue to erode against the US Dollar in the near term ... undoubtedly, it will rebound in the future ... so, your timing will affect the cost (don't forget to factor in VAT if you are buying a new item).