The budget of Sofia for 2018 is already uploaded to the government's Open Data Portal  https://opendata.government.bg/ 
This year, information on revenues, expenditures and capital program of Sofia is in a convenient viewing and downloading format. All Sofia Municipality budgets from 2012 onwards can be found on the portal and can be used for reports and analyses. 
According to the requirements of the Access to Public Information Act (APIA), public sector organizations are obliged to publish public information that they collect, create and maintain in an open machine-readable format allowing for re-use.