No, you may get robbed though, especially at the border having to pay local vignette and road tolls...
It also means you must cross Serbia, again being robbed at the border
UK to BG, approximately £350 in fuel, £380 in taxes and tolls
Sofia - Dragoman -Kalotina (follow road E80)
Border. Entry Serbia. Continue road E80 to Nish (Nis)
From Nisn to Beograd go on highway (toll tax about 15 EUR). Highway goes through Beograd. After Beograd - second part of the highway - toll tax about 7 EUR. Continue on E70. Follow Zagreb. Reach border.
Distance from Sofia to Serbia /Croatia border about 500 km.
In Croatia they have very good highway and again toll tax.
Hope this will help.