Dispense dry laundry soap with panache! FREE PLANS: get some free time, and plan on making this.

Economy:
Per load, we use 45 ml of powdered soap (that's 16.5 g by mass). The powder costs us about 3.6¢ per load. For comparison, liquid detergent is around 20¢ per load, laundry sheets/strips cost between 17 and 23¢ per load, and pods are around a quarter. In term of savings, nothing else comes close to powdered laundry soap (as long as it isn't name brand).

Refilling:
The champagne bottle's capacity is around 800 ml. At five (45 ml) scoops per week, the bottle will need to be refilled once every 3½ weeks. Note that there is such a thing as a bigger bottle.

Soap:
Foca (blue) & Roma (white) are the dry soaps we use. Far and away, they are the cheapest. Name-brand powdered soap is a joke. There's lots of marketing effort going into getting people to spend more for no reason. Cheap powders can be harder to find; they come in plain PE bags, which are usually placed on the lowest bottom of the shelf in the Tide isle.

There's really no 'correct' blend of powdered soap. Different brands will have different properties, and people will have their personal preferences, sure, but there's even more to it than that. Virtually everybody out there will have water of a unique character; depending on your particular water source, you'll find that a different soap blend will be appropriate to your specific laundry/needs. Consider that every water source will have a different pH, a different hardness, and a different cocktail of dissolved minerals mixed into it. And for you city rats out there, none of this is to mention the deliberate chemical additives put in there by The Man, like chlorine and fluorine, which will even further alter your water's washing properties. Thus, don't take anybody's advice. Do your own experimenting, and find your own suitable blend. Oh, but do take this one piece of advice: liquid laundry & dishwasher soaps are for chumps, and soap pods are only for complete morons. Spare me your rationalizations about convenience—I speak only mathematically verifiable truth.

Remember, fellow consumer: you and I make a vote with each purchase. People who are willing to pay several times what a product is worth for nothing but a well-marketed convenience hurt us all. Such foolish spending is a reckless behavior that alters market expectation, perception, and culture, and which ends up changing our available buying options (the supply). Just as democracy is made inefficient by ignorance, so too is the consumer market ruined by wasteful fools.