1 to 3 standard size cards for $1.25 or whatever the current USPS charges are

Relic's, Materials, and thick cards will depend on the thickness of the cards for how they will ship

ebay standard labels are only insured up to $20 

USPS Ground Advantage

4 or more cards will be $5 for shipping 

Spend $50 and USA shipping is FREE!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!