>>1033035normally i'd rec a used rigid mtb for a cheap bike to learn and commute on but considering a few flights of stairs you want something light and easy to carry.
So a mtb or a hybrid are probably off the cards. They tend to be heavy and a cunt to carry.
A traditional horizontal (or near horizontal) top tube to shoulder the bike easily would be preferable.
You probably want a road bike, as light as you can afford. Cheapest option is used.
Do you have a local auction site? Link it and give your size and ill have a look for you.