Where im from, a 20 peice is 2 grams in which you pay $20 for. Iv never had to pay more then $10 for one gram unless its rare buds in which i pay $15 for a gram.

1 g-$10
2 g-$20
3 for $30 OR 3.5(half quarter) for $25-30 depeneds on what your dealer charges.
7 g's- $45-60 depending on who you get it from
14 g's-$80-100
28 g's-$170-200.