I used to play Duel Links and shortly Master Duel after it came out. I don’t anymore but hopefully this will help.

If I was going back to the game, I’d go to look for budget deck lists and seeing what ranks up easily. Most of the community is on Discord and Reddit, as well as YouTube (yugitubers and alike) so I’d go and look there.

I’d also go look for some easy farming methods. These usually come in a form of a current event (IIRC in MD there are these “festivals” for each card type, such as Synchro Festival). These events are usually a very easy way to gain a lot of gems for not much playing.

It is what it is. TCG paper Yu-Gi-Oh is even more expensive than MD.

DL is arguably cheaper but it’s been a long time since I last played (2021).