To lower that with a significant up front cost, you could buy the drives yourself, perhaps shucking external ones and then send them over to Vapornode https://vapornode.com/storage-vps so they can host it at 10 USD a month per disk. If you have a Fry's close by, they have 8TB units for 200, recently Best Buy had them for 180 but I think that ended. So that's 200 + 10 / month vs 4.5 * 8 = 36 USD / month, you are saving 26 USD a month, it takes eight months for this to be cheaper. I would say it's not worth it because replacing dead disks are on you but it's up to you. Also getting many smaller disks make for better RAID.
Finally, lowendtalk regularly has discussions on bring your own disk providers. You need to know what you are buying but it's doable.