Sofia Zoo has a large territory and it is nicely organised, so we were able to see lots of animals without doing detours or walking for miles. When we were there in Spring 2019 some of the areas were being redeveloped, so maybe when you visit next the zoo will be even prettier.
Admission prices are very affordable , especially if you compare it with London Zoo, where you need to spend £100 for a family of 4 before getting through the door. I find London prices for kids attractions sometimes prohibitive, so it was a relief to see that Sofia was not heading in that direction. Sofia zoo tickets costs £2.00 for an adult and £1.00 for a child 3-18. Kids under 3 are admitted for free.