You are right Bill, the DIY stores are expensive.
There is a reasonably priced builders yard in Varna, it is
Here
The L shaped building is the one you are looking for.
It is on the right as you head down the hill towards the lake. Doesn't look like a builders yard until you enter the compound and drive past the parked lorries, some of which are for hire with a driver, first you will come to many concrete products on the left, and a bit further down is a loading bay, usually has pallets of cement on it, enter through this door and have a good wander around.
We bought most of construction materials from here, apart from bricks, blocks, tiles and timber, loads of timber yards around anyway, and prices are fairly consistent amongst them.
Just remember that most of the timber you will see here was growing the previous week! So try to buy from stacks that are under cover, I'm always very picky and select my own timber, some yards don't like this, so go else where if they resist.
Hope this helps.