Here is where I get my cards:
yugiohmint
ebay
tcgplayer
Those are the top 3 places to get your yugioh cards online. I would trust yugiohmint the most, they give you 7% discount if you enter a certain password during checkout, plus they have INSANE cheap prices for foils, the foils in the site cost as low as $0.28! But the shipping prices are expensive, so don't buy heavy stuff like tins, just buy singles.
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Walmart
You can search for it on websites such as Ebay or Gumtree (UK) and you'll probably find a bargain there. You can also search and compare the prices on Buying Cheap (UK).
The website roastgoose. It's cheap, but the shipping cost is high.
You can get a cheap PlayStation 2 memory card online from Amazon for roughly $13. You can also purchase used PlayStation 2 memory cards from used game stores such as GameStop.
There is a Daily Echo in Boscombe that sells Yu-gi-oh. It is also very cheap . I buy most of my cards from there. There is also a tornument every week on Thursday and Friday at Buefort Community Centre in Boscombe. This is near Stourfield School.