Expect .50 for each additional item in shipping unless it changes you from an envelope to a bubble mailer.  

I will have a ton of old school cards in my store soon as I look to sell a life long collection and a store I bought out to pay off my car 😀

Cards are generally lp or better unless marked differently.  Low value cards get scanned for obvious issues. 

I ship in shipping shields up to about 10 dollars