ML grew up in the countryside with nothing and now goes to school in the city:
- Dream High (school / singing / dancing) - Song Sam Dong (there's another ML who also isn't rich)
- Hwarang (historical)
Dramas where it's really emphasized that the ML is poor:
- My Only Love Song (time travel) - ML is a broke con-artist with a good heart
ML is not a typical heir or rich guy:
- Healer (action / reporters) - ML is a loner with a secret identity due to his job (man for hire); he lives in a sparsely furnished secret space in a construction site; he's saving up to buy his own island one day so he can escape and he's rumoured to take any job that doesn't involve killing someone
- A Love So Beautiful* (school / slice of life) - mostly raised himself (older son of a single mum who works in another city), he does become a doctor through his own talent
and goes off to Beijing for a while
but even as a doctor he needs to sell his car when he decides to secretly finance the FL's dream
- Because This is My First Life (slice of life / cohabitation) - ML works at a dating app company; he took out a large loan in order to buy his apartment that will take decades to pay off
- Bring It On, Ghost (supernatural) - makes money by performing exorcisms (fighting ghosts) because he has the ability to see them and needs the money (he's saving up to get his eyes "fixed" so he won't be able to see ghosts anymore)
- Fight for My Way (slice of life / friends to lovers) - ML was a champion fighter in school but now is a pest exterminator
- Gu Family Book (fantasy / supernatural / historical) - ML is found as a baby abandoned in a river and adopted by a rich family, but his adoptive father is killed and he is cast out
- In Time With You** (slice of life / friends to lovers) - ML is the manager of an airport check-in team
- Live Up to Your Name (time travel / medical) - renowned oriental medicine doctor in ancient times was born a commoner, so even with his immense talent he can't advance beyond a certain level in his career; although he is often asked to treat wealthy nobles, he can't spend the money he receives from them
- Ms. Perfect (thriller?) - one ML struggles to succeed in his mid level office position, the other ML is an attorney who struggles to find a permanent position - he wears knock offs and depends on rich sugar noonas to buy him nice things (clothes, his car, etc.)
- Pinocchio (reporters / revenge) - ML is the son of a firefighter but is separated from his family and adopted into a middle class family on an island that can only afford to send one child to university; although he's incredibly intelligent he has to pretend to be stupid for plot reasons;
he lets his adoptive niece be the one who goes to university;
he drives a cab
and eventually becomes a reporter
- Queen In Hyun's Man (time travel) - ML is not a royal in ancient times (I forget his exact position in society, but he's educated) and has no position, identity,
or wealth (thanks for the update Czakhareina) in modern times - School 2013 (school) - MLs are trouble students and their families aren't rich
- Strongest Deliveryman (slice of life) - ML is a talented food deliveryman who moves to a new neighbourhood every few months
- Weightlifting Fairy Kim Bok Joo (slice of life) - ML is a student athlete (majoring in swimming); he grew up with his middle class aunt and uncle
- Witch's Romance (noona) - ML co-runs an errand service with a friend
All of these have a significant amount of romance except maybe School 2013.
* Chinese drama
** Taiwanese drama
