newegg has some pretty good deals on Verbatim DL and 8X +R discs as long as you don’t mind rebates. My success rate with Verbatim rebates has been 100%.
10-pack of DL for $20.99 - $8.00 MIR + $4.99 shipping = $17.98. Link here.
50-disc cakebox of 8X +R for $18.99 - $8.00 MIR + free shipping = $10.99. Link here.