Rarity

From CMC Wiki

All cards have a rarity value. For cards available in booster packs, it determines odds of the card appearing in a pack.

There are three levels of rarity, as follows:

Common	1 to 60
Uncommon	61 to 85
Rare	86 to 100

Cards of rarity 101 also exist. These cards are never available in booster packs, although not all cards unavailable in booster packs have rarity 101.

Prime, Clash of the Webcomics, Principalities, War of the Webcomics and Mechanical Chaos booster packs contain 9 commons, 5 uncommons and 1 rare.
Unknown Expeditions and Masterwork Tools booster packs contain 3 cards of assorted rarity, but with cards of higher rarities appearing less often.

The buy and sell values that the Public Store uses are directly related to rarity for most cards, but are usually vastly different to the values when traded amongst live players.

Buy value = floor( rarity * √rarity / 3 ) + 5
Sell value = One fifth of the buy value

Cards unavailable from booster packs, such as those of the Voucher, Event, and Secret sets, have a buy value 2000 points. If they have a rarity of 101, they have a sell value of 600 points, otherwise they sell for the regular amount.