It's fairly simple to achieve, you just need your brickwork to be sound in order to match up to the existing above, essentially the building above from what you say is lintels rested on corner pillars?
You will still need a cavity in the walls and the correct air bricks to keep moisture out, and allow air to pass under the floor. As for price that's not something I can tell you off the top of my head, I don't know the area you live, materials and labour prices vary a bit across the country.