For dual layer Verbatim, $1.25 or less per disk is a good deal.
For dual layer media under other brands, never pay more than $0.75 per disk.
So, for example, a 20-pack of Verbatim DL for $25 would be a good deal.
On the other hand, you shouldn’t pay more than $15 for a 20-pack of any other brand of DL media.
Those are just my personal guidelines. Others may allow for a slight bit more inflated pricing.
Keep in mind that my pricing on the Verbatim assumes 2.4x-6x disks. 8x-12x disks will be more expensive.