Is it really two separate units or more like an "all-in-one" machine? I havent seen a over and under,all in one cabinet washer-dryer that was any good.People only usually buy them because they havent got room for anything else (i.e. in a closet).So many engineering shortcuts are taken to get everything into that narrow cabinet that the end result is a pretty much universally crappy product,whether its Maytag,whirlpool or frigidaire.
If its actually "stackable" units,there would have to be a front loader washer,and these are expensive machines.To find one two years old in operating condition for 300 bucks would be a good deal.