TDK 61611 8.5GB 8x Dual Layer DVD+R Media Spindle (50-Pack) for $14.99 shipped after code EMCPFWW38 and this $5 rebate.  Here is a screenshot for your reference.  The dual-layer blank DVDs tend to command a significant premium over single-layer blank DVDs and store more data.  Most places have this 50-pack spindle for about $33.