You're looking for "TTL". It's a common feature, but will need to be compatible with your camera manufacturer.
If you want cheap wireless, a trigger and a couple receivers from Cowboy Studios runs less than 20 USD- dunno how available that particular brand is in Europe, but there are a lot of similar ones available from other makers. What you've seen in the YT videos is an optical trigger- most have them these days, and they're pretty reliable, but need line of sight to your camera and sometimes don't work great in bright ambient light. Unfortunately, both of these are going to be a "dumb" triggers- it just tells the flash when to go off, it doesn't control its settings. If you want to use TTL off-camera, it takes a flash commander/pocket wizard with that functionality, which isn't cheap.
At that price, you can get pretty much any Yongnuo or Neewer flash you want, or maybe a used first-party flash. If you want to use it off-camera, though, you're also going to want lightstands, brackets, modifiers... you can still do it in that budget, but it's a bit tighter. Something like this won't last forever, but will give you a pretty good start for a two-flash setup (just the one I grabbed in the US, there should be something similar on a website local to you). You can go with optical triggering if the budget is too tight to add a cheap set of radio triggers. You'll still have plenty of budget for at least one Yongnuo or other third-party flash compatible with your camera (including TTL, but without a compatible commander you'll only have TTL mode available on-camera, it will just work in manual mode off-camera), possibly two if you find a deal or get a slightly older model.
What camera do you plan to use it with? Any features on the wish list besides TTL? What kind of photography do you plan to do with it?