I recently found the website which lists the bailiffs in Bulgaria, and the properties that they have for sale as a result of bankruptcy/repossession.
I'm not sure how easy it is to actually to do a deal. It's all in Bulgarian, and the process seems quite low-tech. The site just lists the property details, the bid process, the minimum price, and the time the auction is active. Then you have to decide on your bid, and submit your offer to the court (with 10% of the bid deposited to the relevant bailiff's bank account). At the closing date, they review all the submitted bids. And I guess you either win (and pay the rest of the money within a month), or you lose and you will get your deposit returned. Probably the best option is to engage a Bulgarian attorney to act on your behalf.
Some of the unfinished houses look quite interesting for the money. And there appear to be farmers who have lost multiple plots of land in particular villages, with each plot being listed for around 1,000 or 2,000 euros.
The website is here:
https://sales.bcpea.org/properties
Bansko Blog (by a Brit expat writing about Bansko and skiing) has an entry about Bansko property. This includes a video with a local realtor discussing the process of buying via this site. He seems to be a fan, and says that properties are available at a substantial discount to current market value. You'll probably find this video more helpful than my short description!