Stamps are fine.

A small bubble mailer up to 2 ounces (enough for 1-2 chips, depending on the chips) is 63 cents.

28 grams = 1 ounce. Most casino chips are in the 10 gram range, so you should be able to get 2 chips + packaging material for 63 cents.

Prices go up soon, though (May 27th, I believe).