I think people are a lot more familiar with Chinese phones these days than when we first started doing these threads 5 or 6 years ago. Buyer beware but generally the quality level of phones like Xiaomi are on a par with the traditional flagships nowadays.
Most people buy from the following but there are many others:
Aliexpress (Check each sellers feedback) - http://www.aliexpress.com/
Honorbuy - https://www.honorbuy.com
Banggood - http://www.banggood.com/
Pandawill – http://www.pandawill.com/
Dealextreme – http://www.dx.com/
and of course most of these phones are on Amazon aswell, check Amazon.fr, .es, .de etc for better deals. Also a lot of stores have European warehouses for quick delivery/no customs fees:
Honorbuy EU store being one of the more favoured sites of late for quick delivery. https://www.honorbuy.com/28-eu-direct
https://www.gizchina.com/ is a good place to see whats being released currently, every month they do a Top 5 Chinese phones under $500/$250/$100.
https://www.gsmarena.com/ is a great resourse for comparing specs between models or just ask here, enjoy.
Anything else to add while I can still edit the OP?
EDIT2: Good call Corkie: