When stopping at a shop, there is always one cheaper discounted card on sale you can buy. When a card is on sale in the store, how much of a discount are you getting? For example, if a card costs 200 gold normally, how much would that card cost when it goes on sale?
According to the wiki, cards "on sale" are sold at a 50% discount. The Machine Learning pictured for 89 gold would have cost 178 gold normally, which is consistent with the cost of a rare card on Ascension 16+. Rarer cards are more expensive and get bigger absolute savings when "on sale" - buying a common on sale might save you 30 gold, while buying a rare on sale might save you 90 gold.
