I wouldn't buy any if i were you. They're more fun to find in circulation! But in case if you wanted to invest, or couldn't care less about finding them... I'd pay 3-15 c per penny, and 8-20 c per nickel. (The older the coin, the more you spend.)
Dealers typically pay 2.5 to 3 cents each for wheats.... you should be able to buy them in bulk for 5 cents each I don't think they pay any premium for circ jeffersons... you should be able to find them in circulation.
I have a can of wheats I found in circulation. I have higher grade coins in my book I also found in circulation. Jefferson nickels can be found in circulation, including war nickels.
Which could be said for any coin. Let's think varieties and such - leave the minty ones to tone in their holders