Ground floor, so concrete? Concrete should be fine. But regular floors would be able to hold up to 75g or so with out too much worry.
I believe cinder/concrete blocks are sold in any country, so you should be able to find them in a large hardware store. I would say that if you stack the blocks, ei want to make it taller, you should put a full length wood board between all blocks, not just a 2x4. That way they all put pressure on the board and hold it more steady.