Hey there, Spankymcbob1!
Unfortunately, I cannot comment on the prices of the products. However, I'd strongly recommend you to consider buying RAID/NAS-specific hard drives. They are specifically designed to withstand the workflow and the 24/7 environment of a NAS enclosure. Such HDDs incorporate a specific firmware and optimized features that improve the compatibility and reliability of the drives.
If interested, you can check out the WD Red drives here:
http://products.wdc.com/support/kb.ashx?id=66BjIj
Under compatibility, you can see what other WD drives are compatible with your NAS enclosure model.
Hope this was helpful. Keep me posted if you have more questions regarding the storage configuration!
SuperSoph_WD