Ten 16X / 120 minute Memorex = $8.88 Made in India
Ten 4X / 120 minute Memorex = $11.88 Made in India
Ten 16X / 120 minute different brand = $7.88 Made in Taiwan
Ten 4X / 120 minute different brand = $10.88 Made in Taiwan
I bought one each box of the Memorex. Using for recovery disc on 2 different ASUS Win-7 64 bit laptops as recovery disc as a Windows disc did not come with.
Or just that 4X is rather slow, and used mostly by near-obsolete drives. Probably way outsold by the 16X ones. So just the usual sales volume thing leading to lower prices.
You didn’t specify whether the DVDs were +R, -R, +RW or -RW. That could make a difference in the pricing, and also in compatibility with your burner, although most newer burners will handle all of the above types.
ETA: Also, if the discs are LightScribe discs, which allows you to burn a label on the non-data side, they would cost more.