Lets think of it this way without knowing the size of your quilt. Say 50"x75". That will take 176 5" pieces or 5 Charm packs (you can't split one).
That is about 3/4 yd of fabric. I found a price of $9.50 per pack.
The 5 then will cost you 47.50 plus shipping if ordered.
If you buy the necessary yardage you will need about 3 yrd total. At 9.50 per yd this will be 28.50.
On the other hand the additional cost may be worth it in saving of time and variety of fabric.