That would depend on what species tortoise and how big it is, Do you need the table to be a closed chamber for a baby or a species that needs high humidity all the time or is it for someone that doesn't need quite that much humidity and you can do an open top table. There are several ways to make one, you can start from scratch and build it which will cost anywhere from $50-300 on wood and supplies depending on the size and other details. Another way would be to find an old book case and get a pond liner or tarp of some sort, take the shelves out and wrap it up in the tarp, this way is going to be cheaper, as you can probably find a free book case online or at least a very cheap one, but will already be a set shape and size, if you make it yourself it will cost a bit more but you can create it to fit your space, rather than rearranging a space to fit around it.