I fear you will only waste your time,patience and money,the UK is hard enough to set up a business and be ' in profit ' and Bulgaria is ten times harder,in making money,red tape plus the language barrier.
Have you stayed for any length of time here in Bulgaria? or have you your UK business head on?I dont know where some Brits have their prices from regarding LPG systems and fitting,but i think they are being ripped off big time,as you know there are two different systems,carb and injection,i paid for a complete new system and fitting (ok a year and half ago) 400 lev,that was for a 2ltr petrol carb conversion,dual fuel switch over,never had a problem with it ! The injection price was 1400 lev,alarmingly more pricey,if you can beat or come close to that price,then go for it,if you can find premises safe and secure,with enough customers in that catchtment area,usually nearly every garage does or knows a mate that installs LPG/petrol systems in Bulgaria mind you,you might also have to deal with local heavies etc.
As for a mechanic or garage to Brits ?If you perhaps move/buy near to VT,you might just have a chance,IF you charge Bulgarian prices,many foriegners,i say foriegners instead of Brits,because business people fromdifferent places come over here thinking they can start up,in their trade or proffesion only to go home a year or two later ,with a big hole in their pockets !
Perhaps before outlaying money etc,you could possibly rent and get a 'feel for the place' as many have put all their eggs in one basket and suffered the consequences.
A good cheap luxery 4x4 mechanic might go down well,also Merc and BMW to the no necks.did someone mention window film ?like the ' mafia ' use,and everyone seems to want to copy,even in their rusty old 'go faster Lada's' ,maybe again but i doubt it,17 year olds are doing this for 40 lev per car (£20) fitted....