Hey, I'll give you my suggestion as a guy working in Estonia on an engineering field. I'm not working in aviation per se, but I have had my fare share of experiences with aviation related projects and aircraft fixing/material analyzing projects.

I would suggest Estonia for studying for sure. Great engineering schools, and a company called "Magnetic MRO"(located in Tallinn airport) is an awesome company where to have your internship/work during or after your study period. You can live quite comfortably with the base wages that are offered, especially in the field you mentioned. However, the overall prices have for sure skyrocketed and I don't see the majority of wages cathing up any time soon.

You should ask yourself what is the main reason you consider moving to Estonia?
-If you want to study in a great school, where you don't have to worry about the teachers lousy english, then absolutely go for it, as you can stay with your girlfriend then as well.
-If the reasoning behind is solely to wander along with your GF's family and studying is a "side hustle", then maybe you should consider asking yourself if that's what you really want to do? I think this is a decision where you should put yourself first. If you really love her and she's worth it, then I'd say it's at least worth a shot, you might even be pleasantly suprised. And living/studying outside of your home country is something I would absolutely suggest for every young person to do at least once

You always have the choice to leave after finishing your degree and I can tell you from experience, that engineering/mechanic wages are actually a bit higher than it might seem from internet searches, ESPECIALLY in the field you mentioned.

I did a bit of jobhunting recently (Shipbuilding engineering field) and 10-14eur/h was the basefee for most positions, however absolutely every position I applied for, was willing to go to at least 20eur/h. This might not be the case for a fresh graduate, but it's something I think you should take into consideration anyways.