Is $10,000 to install return ducts in upstairs bedrooms/hallway a fair price?

I have a very old house (c. 1925, ~2250 sqft) with central air heating. I'm looking to get A/C installed, primarily to cool the upstairs bedrooms. Contractors noticed there are no return ducts in the two upstairs bedrooms or hallway, although the main level has returns in each room. I understand this could make the A/C less effective upstairs and potentially cause positive pressure downstairs. I'm considering several options: installing AC as is, installing a fan to pull air outside, installing return ducts (which seems expensive and requires tearing up walls), or installing mini-splits (which also seems expensive and I don't like the look). I'm looking for advice on the best path forward and if there are other options I've missed. I'm also wondering about the effectiveness of undercutting doors for airflow when the closest return is on the main level, and about the cost and effectiveness of potentially combining mini-splits with the existing ductwork.