Building an addition up or out is far more cost effective than digging an existing crawl space. The crawl space must be manually dug and must avoid undermining the footers of the house foundation. On top of that, you have to move all the spoils to the outside and transport it to a disposal location. This is an unbelieveable amount of labor. Not only that, but when you are done you will have added no resale value to the house. In most cases, basements are not counted as living space square footage in value appraisals.
If you don't want to see your husband for about 5-years while he becomes a miner and digs out your crawl space, you should probably encourage him. But big bob is correct on this. If you must have a basement, buy a different house.