Drives that can write to the double-layer DVDs are widely available, but the discs itself are kind of hard to find. And when you can get them, they're expensive: a single DVD-R double-layer disc will cost you around $5-10, while the more common single-layer media is available for less than $1.
The other problem with this media is reliability. You can get pretty cheap No-name Double Layer Disks but be ready to through up to 80% of the to the garbage can.
We can offer you Dual Layer media from the several manufacturers (Ritek, Memorex, Verbatim) for the best possible prices.

