Since I will be offline from Saturday till Tuesday, here's sth I wanted to write as helpful advices how to get from the airport to the city for anyone coming to Sofia - also the other thread about Istanbul and Steve's enquiry reminded me about this.
First thing buses - the bad news about buses is that they travel from 5 00 am till 24 00, so since the majority of ppl will arrive with the Wizzair night flight - this is not for them. However this is for everyone who will arrive during the day - e.g. EasyJet (speedy) or whoever else.
Terminal 1 (where Wizzair & EasyJet arrives) - The public transport bus
84 runs a frequent service (every 10 or 15 minutes, 0500-2400) between the airport and Sofia University, close to the city center (journey time - 20-25 minutes).
Bus
284 operates between the new Terminal 2 and the university, also every 10-15 minutes.
Tickets can be bought from the kiosk near the bus stop or directly from the driver. Then make sure to punch them once you get in the bus. Tickets cost 1 Lev (which is 0,50 c.).
Both buses leave from stops just in front of the respective terminal. It may take some time waiting - 10-15 minutes for the bus to arrive, or if you are lucky - it will wait for you there.

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This is the cheapest way to get to the center, but as I've already said, since most of the ppl will arive in the am hours, it will be of no use for them.
The other option is TAXI - now here it gets a bit complicated, at least if you care about not being ripped off.

From both Terminals there are stops for TAXIS and there are always taxis waitng, but I'll explain more about Terminal 1 (where Wizzair will land). Terminal 1 is the older airport it is smaller which is good when you arrive, cause it is hard to get lost there.
First of all: here are two very useful links -
SOFIA AIRPORT site and
OK TAXI site.
OK Supertrans Taxi is the cab company that has official contract with the Airport for providing taxi services. There is a special desks in both terminals of OK TAXI where you can go immediatelly after you arrive and they will lead you to the taxi stand, and help you and whatever else info you need about taxis (there are OK taxi stands with signs outside both Terminals)
However since we are talking about 3 am here - I am not 100 % possitive if these office desks will be working - also searching for signs in 3 am is not a very enjoyable business.
Here is another
link with photos of the OK Taxi airport offices and the cabs - Terminal 1 photos start somewhere in the middle of the page.
Now look very carefully at the pictures at the links above - there are several private companies which try to mimic the OK Supertrans logo and look. Beware, cause these "touts" will try to ask you if you need a taxi as you exit the departures area. These guys will seriously overcharge you (like 4-5 times more), so just continue on and don't pay attnetion to them.
OK Supertrans Taxi drivers are not that aggressive - they just sit in their cabs waiting for clients at the stands.

The reason I am writing this is that other companies are trying to immitate OK Supertrans (Supertrans in cyrillic is Супертранс) and you can easily be fooled.
For example - here is the original -
OK TAXI and here are mimics -
immitation one or
twoTwo ways to immediately know which one is the real one: - first is of course the phone number written under the "OK supertrans" logo - 9732121
and the other- even better - you go to it and look at the tarrif list - it is always at the backdoor sidewindow - and you will immediatelly see what they will charge you. If it says 0,55-0,75 leva per kilometer - its OK, if it says - 3,50-5,50 per kilometer - then run away.

If it says even 1,49 per km - like
these guys here - it is not OK, they will be ripping you off.
The prices are shown on the OK taxi website -
HEREThe prices of the other "normal" taxi companies in Sofia are again something like this - 0,55-0,70 lv per km. or even less. If someone tries to charge you more - don't get it.
They are all obliged by law to show the prices at the backdoor side window. Unfortunately (due to our free market economy) the law cannot oblige them to keep prices in specific ranges. SO if ppl are not cautious they may get ripped off. Other thing that Law don't oblige them to do is type the prices in English...
So if you are careful and look the prices - it will be all right.

The ride from Airport Terminal 1 to the center of the city should be sth like 10-12 Leva (5-6 E) or around those - depending on the destination.
Important tip: No matter whether you take a cab or a bus - when you are on your nearly 10-th minute of the ride, you will be on a loooong highway going to the center of the city, and if you are careful and look to your right when you are passing a bridge above a round crossroad you may spot a big sign like this -
This place is where you'll be on Friday night 
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