A few days ago I decided to exchange my cards to Gold and rent the more powerful ones. When comparing cards, you need to take the minimum gold level in consideration.
Let's take the Cocatrice as an example. A Gold Cocatrice starts at lvl 3 while a Regular one needs 5 to reach lvl 3.
Let's check their prices.
If you bought the cheapest ones, you'd need $26.40 to reach lvl 3, while the cheapest gold costs $23.90.
Let's go beyond, Cocatrice gains the Dodge skill at lvl 5, needing 21 Regular cards and 4 Gold cards. Checking the prices again, you can buy a Regular lvl 5 for $102 and a Gold lvl 5 for $95.87.
There are a few others cards this happens as well, but not many.
In my site, https://monster-finder-d7d0d.web.app/, I created a new feature to search for max ratios based on the Low Buy price of Gold and Regular cards.
requested a search field on the toolbar, and it seemed like a good idea, so I added it. Comment what features you'd like to see.
Cheers