Compacting data from multiple cells

I'm sure a similar questions has been asked before, but I am on an unfortunate timeline and am hoping some good soul will be able to help me.

I am generating a marketing report template for my company. I want to pull the square footage of a apartment on one sheet, and enter it in a cell in another sheet. Here's the catch, the sheet I'm pulling from has two cells for square footage, low and high. I want to pull both numbers from their individual cells, and display them in a new cell on a different sheet in the following format;

400 - 500

Lastly, I want the cell to display only the exact square footage if there is not a variance, or nothing if both input cells are empty. I've been using the following formula for when I am pulling from a single cell;

IF(COUNTBLANK(A1),"",A1)

I am relatively new to both programming and especially programming in excel. I like to think I catch on quick, however, and would prefer to learn from this experience. Any help that can be provided would be much appreciated!

Thanks in advance.