I brought my Mobile disco with me two years ago, just in case? in that time I have done a few gigs for Brit bars and a couple of charitable organisations events. IMHO it will not make you a living.
I agree if you have all the equipment then starting your own or joint venture disco may be the way, but in BG thats no gaurentee.
I have taken on learning the BG dance culture also and done a couple of disco's for our village,
With the brit bars you may get your travel expences but in my experience if you ask for over 100 lev for a full nights work, you may not get the gig.
Your main work time would be the summer catering for the holiday makers (The more mature age) and most of the BG venues have sound systems installed.
You could try the big holiday resorts, they may like a UK style disco
As for me.. now I just do village events mainly Bulgarian music) maybe once a month or so and the odd private function. But I have retired here so do not have to depend on the income, if any
Good luck, PM me if you want more info