It used to be much more easy, but since the financial education is pretty bad, for many people real estate is the only viable investment vehicle. Together with this, probably billions of money from the grey economy had to be legalized prior to switching to euro and that created an enormous boost in demand for apartments. The market cooled off since, but the prices remain low (and since the construction activity is expected to cool off too, I don't expect the prices to go down any time soon).

So currently (not only Sofia, but even in small towns) it is incredibly hard for a single young person to buy an apartment. Yes, the interest rates are very low, but the prices are very high. You would need at least 30% in cash, otherwise you would have to repay insane sum to the bank.

Which creates a weird situation as I was considering buying a small apartment at the time (scrapped my plans even though I can finance most of it in cash). It gets exceedingly hard to acquire an apartment as a young single working person, even when funded by a mortgage. On the other hand, at some point, probably half of the apartments were bought 100% in cash, by people who don't intend to live there and the demand was insane too, a building next to mine was sold out already before the construction of the first floor was finished, there are some kind of discounts for early buyers.

And contrary to what other people say, it's not just Sofia or Plovdiv or Varna like that. It's everywhere. In Ruse for example, which is a town of \~130k, the last 2 years saw more construction activity than the previous 10 combined, they were/are building a whole complex of eight 11-story residential blocks close to my parents home for example. A huge number of new residential space all that while access to it (at least by poorer folks) gets harder and harder.