Depends. I can find Dreamcast, Wii, WiiU, NES and SNES for under 100€ each at an online reseller. Considering they want to make a profit off these consoles, they will probably pay you 50-70€ per console. Hardly anything to get excited about.
When I said that, I was thinking about certain games that despite being 20 or even 30 years old have gained value for some reason. A lot of N64, Saturn and Dreamcast games are fairly hard to find and that reflects in the cost. Games like Conker's Bad Fur Day or Shenmue II or really any decent games that came out at the end of a console's life regularly cost more than the system they were released on, today.
I saw a NES game called Bucky O' Hare. Never even heard of it, in a CEX near me being sold for £120. Just mental!
Xbox One, PS4 and Switch (+ Many Retro Consoles)
'When the people are being beaten with a stick, they are not much happier if it is called the people's stick'- Mikhail Bakunin
Prediction: Switch will sell better than Wii U Lifetime Sales by Jan 1st 2018