If you are too lazy to walk up to the Rila lakes hut you can go to Vada hut, close to Govedartsi village and take a truck GAZ or a van WAZ. Both vehicles are Russian make and the abbreviation shows factory where they were made.
Do not expect comfort :) You will travel trough a rough road with no pavement and you will sit on a bench and jump up and down most fo the time but I think it is part of the expirience.
The vehicle leaves at 9 in the morning. Depending on the number of passengers it can be either the truck or the van.
If you are with the truck, as I did, it takes approximately the same time as walking to the Rila lakes hut, about 2.5 h. I heard that the van is faster.
We paid 10 leva per person (EUR 5).
If you are too lazy to walk up to the Rila lakes hut you can go to Vada hut, close to Govedartsi village and take a truck GAZ or a van WAZ as I said in my other tip. Besides that option you can try some horse back riding.
The horses are next to the trucks and I think that the price for them is more or less negotiable. I did not ask because I did not intend to go up to the Rila lake hut by horse.
What I saw some people do was that they had put their backpacks on the horses, paid some money to the people who take care of the horses to take their things to the hut and continued hiking up to the Rila lake hut.
So, if you still want to walk but you are not keen on the idea to drag along your backpack you might consider that option.
To get there from Sofia, we took the train Sofia-Kulata at around 7:30 am and got off at Dupnitsa at around 9:45 am. The bus station is right next to the trainstation, and from there we took a minibus that goes to hizha (hut) Pionerska. You have to tell the driver that you're going to hizha Skakavitsa so he will leave you at a crossroad from where you take a dirt road and then a marked (in Bulgarian) path to Skakavitsa. From the place the bus leaves you it's approximately 2 hour's walk, and the last one hour is a very steep path by the cascading river.
One of the ways to get back is to walk to that crossroad and wait for the bus which should pass a little after 12: 30 and 15:30 every day. Still, the safest way is to call the driver (Kalin Gelev, phone numbers 0885 148906, 0896 778512).
My advise: get a map and study it well, have the transport arranged, learn some Bulgarian, or at least the way the names of the huts are written in Bulgarian - that's a must if you don't want to get lost. If you're not experienced mountaneer, don't go without a more experienced companion, and even better, a guide.
Beside the 'Rilski ezera' hut there are horses/mules and jeeps. The horses can transport you to the other side of the lakes (Bubreka lake). We didn't try that, but heard that it was 20 lv per person. By jeep you can get down to civilization, althouth I heard that it's illegal for motor vehicles to offer transportation, as the hut is within the boundaries of Rila National Park...
It was easy to purchase a bus ticket in Sunny Beach to Sofia. I don't remember the price anymore but it was very cheap. Everybody gets a seat number and our seats were in the back row and we were wondering if the ride would be bumpy and make us sick. Fortunately it was a smooth ride and we had no problems. You should have seen the faces of the two young men who sat next to us, when they saw that they should have to share the ride with two elderly women! It was so funny!
As I have already written in other tips getting from Sofia to Rila wasn't that easy. We chose a train and finally managed to find the platform and got where we wanted but it was no thanks to the locals, who were not helpful at all. The train ticket was very cheap also for a trip of some 125 km. Here I have to pay more to get to the city centre!
If you look at the picture you will see that it is written taxi on the front and there is a mobile you can call to order it :)
I did not see that one on the Vada Chalet but close to Rilski Ezera Chalet. I do not know what was the starting point of that taxi but if you need a transport to the Rilski Ezera Chalet you might call and ask.