The reality is PAL NES games with any sort of name recognition sell for ridiculous amounts of money. I don't blame the sellers at all, it's buyers with zero idea what things are actually worth who keep pushing the prices up. The NES was nowhere as near popular here as it was in North America but believe me when I say it sold well, there is no shortage of games or consoles and there's no reason whatsoever for something like Metroid to cost £30. Definitely stick to American games. They can still be quite expensive unless you import, but even if you find them on UK eBay they're usually much cheaper than PAL games.
I'm still super grateful for that man, you really did save me a ton of money. I'm not exaggerating when I say it would have cost like four times as much to buy them over here.