Since the OP is British, I would suggest he consider supplementing his language teaching (which is going to be replaced by computers in the near future for serious learners, IMO, with real teachers kept around only to serve as scapegoats for when lazy kids don't learn anything) with some sort of work that leverages his British background. For example, real estate sales, package tourism development and management, sales and advertising consulting, etc. Obviously, there's already British ex-pats in Plovdiv etc doing this, but should be room for more.
I spent 2.5 months recently wandering around Bulgaria, mostly small towns and villages. Huge potential for tourism or cheap retirement homes for elderly British with limited pensions, but almost nobody speaks English in these small towns and they haven't a clue as to selling to the British. When I was at Yagodinska cave, for example, I heard lots of Russian being spoken by other tourists, but no other foreign languages. So clearly they are able to sell tourism services to Russians but having problems with other nationalities.
I spent 2.5 months recently wandering around Bulgaria, mostly small towns and villages. Huge potential for tourism or cheap retirement homes for elderly British with limited pensions, but almost nobody speaks English in these small towns and they haven't a clue as to selling to the British. When I was at Yagodinska cave, for example, I heard lots of Russian being spoken by other tourists, but no other foreign languages. So clearly they are able to sell tourism services to Russians but having problems with other nationalities.