I have hopefully ironed out most of the issues now, so cards like
Volrath's Stronghold should no longer show up as 0.02. I have also improved the way we match specific printings to Cardmarket prices, so it should pick up the correct printings more often. Unfortunately this isn't perfect, but it should be significantly better than before.
Regarding finding the cheapest versions: The deck price on the Overview tab will always use the cheapest versions, no matter which printing is shown under Details. So if you just want to get the total minimum deck price that should be the best approximation we have for that. If there is a cheaper version of a card it will say so when you hover over its price on the Details tab.