Hi J & K,
The cheap way from Vlas to Sofia is by train. Note that trains are too old and slow. The journey takes about 6-7 hours. The nearest train station to Sunny Beach is in Bourgas, so you would need to get a taxi from there to Sunny Beach. Train cost 20-23 levs Taxi cost not more than 70 leva. Try the Bulgarian Railway Website:
http://www.bdz.bg/I would say the best option is the coach from Sunny beach / Bourgas to Sofia. After arriving in Sofia, take a taxi to the Airport Best to go to the OK taxi Should cost you about 14 lev from bus / train station to Airport The coach journey takes 6 hours. Cost 30 levs The Sofia bus Website is:
http://www.centralnaavtogara.bg/cbs/hom ... enDocumentThe other options but not so cheap is to book a private door to door taxi transfer to Sofia. The taxi journey takes 5 hours as Sofia is 390 km. away. Recommended for transfer to take a look here:
http://airportpickup.tripod.com/sofia_a ... sfers.html My recommendation is to this company because I used them many times and always been happy with their service, but I flew only into Bourgas airport.
Also can fly to Sofia from Bourgas Cost from 33 euro Check here:
http://www.air.bg/Hope it helps you