Mine only takes powdered detergent but it takes so little of it a box lasts a whole year. The clothes are much cleaner too. It’s one of those appliances that can be expensive but worth every penny.
I'm using liquid, but you're right that they use much, much less than the old type of washer. And it'll hold a good deal more cloths in a load.
I got my Maytag at the Sears "scratch and dent" store for quite a bit less than it would have costed had I bought it at regular retail. So far, so good but I haven't had it long enough to really judge the performance.