Need a mediocre gamer for Sims 3

Hello everyone,
I have a girlfriend living in UK (I live in Denmark), and im looking to get her a PC that can play her Sims 3 games at a smooth framerate, although not necessarily with maxed details.

As im not from UK I dont know many websites that sells PCs, and I cant find a forum that has a buy/sell-section what so ever. Also, the pricetag in UK seems way higher than here in little Denmark, which is why im also interested in used/refurbished PCs.

Like said, the system must be able to play Sims 3, and if it comes with a monitor aswell that would be awesome (although not a must), so I guess a mediocre gamer would be fine???

I hope someone can help a lost scandinavian.