Maybe you should try it out yourself.
Usually, it's hard to find cheaper DVD media in US, and it's even harder to find the same media as it is in Taiwan due to various surface printing.
The Verbatim 4X DVD-R is currently on sale at Bestbuy.
It's 25pcs in cake box for 14.99 plus tax with free shipping.
It's a great deal.

If you want to buy something really cheap, try www.supermediastore.com
or
www.meritline.com

They usually sell various sample packs for your testing.

You can also read product reviews about 2500 or 2510 on NEWEGG, some users would also post blank media they are using there.

PS: Do NOT try CompUSA and LiquidVideo (CC) branded media. I've tried them on my Optorite dd0201 and Benq 800A. They are really poor but just a little bit cheaper than other branded ones.