I am going to use 22 liters as the volume of the bag rather than 20 quarts for two reasons. First the American and British quarts are different sizes and I don't know which to use and secondly the conversion between length measurements and volume measurements is simpler in the metric system than it is in the American or Imperial systems. The one conversion factor I remember between the two systems is that there are 2.54 centimeters in an inch.
The conversion between length and volume in the metric system is that one liter is 1000 cubic centimeters (cm3). Thus 22 liters is 22 1000 = 22000 cm3 and hence
Thus at $25.00 per cubic yard 22 liters of dirt would cost
$25.00 0.0288 = $0.72
Hence purchasing the soil by the yard is a better deal.