The mains supply in BG is, at least similar to, the Continental 2 pin system. The regulations are therefore substantially different to the UK. Within a reasonable travelling distance of where you live there will not be enough Brits. to provide you with a living. There may be some work with Commercial Developers, but for that you will need to be fluent in Bulgarian and the probably the codes of practice. The quality of most existing domestic electrical is very poor, so your public liabilty insurance would need to be good and probably your health cover too!
Most Bulgarians are finding it difficult to make a living and the population is dropping as people move abroad to try and find work. Hourly rates here are low and the willingness to pay them very low.
Think carefully and do lots of reasearch before you burn your bridges for a life in BG, in which a local income is essential for your existance here.