How to get to Bulgaria?
All forms of transportation are possible to get to Bulgaria. Your choice will depend on several criteria such as your budget, the amount of time you wish to spend, your family situation, etc.

By airplane
The main European companies operate in two airports in the country, Sofia (scheduled) and Varna (charter flights). As an example, the daily flight London- Sofia takes about 3 hours. Internet is the best way to find your ticket. Search engines allow you to compare availability and prices of several companies simultaneously. For example, you can check:

By coach
A couple of coach companies can bring you as far as Bulgaria .You will travel in confortable air-conditioned coaches equipped with folding backrest seats & seat belts, DVD & audio system, WC. However, the major inconvenience is the length of the journey which takes more than 45 hours and the annoying waits at the country borders. Also, the price varies depending on the companies:

By train
There are no direct lines between UK and Bulgaria. Moreover the trip is long: around 55 hours with several changes for an exorbitant price. For example, a one-way trip from London to Sofia costs approximately 280 £!

By car
Situated at an approximate distance of 1500 miles, the trip requires less than 30 hours by the quickest routes. The time depends on the traffic and weather conditions. Normally the trip would cost you about 350 £ per vehicle in petrol and tolls. The best itinerary is to pass through France,Belgium,Germany,Austria,Hungary,Serbia-Montenegro and then on to Sofia. Another possible route which avoids all these countries is to take a boat from Italy to Greece (approximately 15 hours) and travel up to Bulgaria. A one-way ferry crossing for a normal vehicle and two adults without a room would cost you about 200 € or 140 £. For more details, consult the following sites:
Don’t forget that there remains some 800 km to Sofia. It is and interesting option since the Adriatic crossing is pleasant and you also have the opportunity to cross a part of Greece. However, it is a long and onerous trip.