Game under 3 euros suggestion?
No game is perfectly valid suggestion, but be constructive if you can...

Depends what genre you like, and I'm assuming you're talking about prices during the current sale?
A lot of adventures are under 3 Euros, e.g. Shardlight, Technobabylon, Resonance and Primordia.
The witcher 1 and 2 are also both under 3 Euros.
If you like rpgs, there's also Albion (old, but good) and the two Star wars: Knights of the old republic games.
If you like Star wars and shooters/lightsaber combat, the Jedi Knight games are also very good and currently under 3 Euros.

Just buy something you'd like to play right now. No point hoarding stuff you're not really interested in.

Anyway, there's a great list here, made by RWarehall.

Gabriel Knight: Sins of the Fathers
Master of Magic
Sid Meier's Colonization
Thief

Just above:
Bastion

You seem to like RPGs, so I highly recommend some Spiderweb games if you don't have them already, great value for the price, very decent old school isometric RPGs, but still easy enough to get into :

- Avernum : Escape From the Pit (2.49 $).
- Avadon : The Black Fortress. (2.99 $).

D&D Dragonshard is 2.19

Is King's Bounty any good?

- Unreal Tournament 2004 Editor's Choice Edition
- Psychonauts
- Clive Barker's Undying
- Serious Sam ( both the first and second encounter)
- Witcher 1
- Stacking (two Double Fine games in the list, I know)

Alpha Centauri, any of the Wadjet Eye games, King of Dragon Pass are some of your choices.

I like it a lot. If you enjoy the art style in the screen shots, turn-based strategy, and RPGs, it's a good buy.

Forgotten Realms: The Archives - Collection Three is €1.79 at the moment, and contains Dungeon Hack, a game that looks and plays similar to Eye of The Beholder series but has randomly generated dungeons (with parameters that can be set before the game).
As someone who usually doesn't like RPGs I find this quite accessible and fun.

There's also this thread:
https://www.gog.com/forum/general/hidden_gems_recommendation

Thank you.... Any more suggestions?

It was recommended to me and I bought it some time ago. Haven't played it yet, cause y'know.... backlog.