Thanks for the reply. I hadn't thought about the fact that increasing the capacity of the SSD may be more economical as a whole. As it turns out, it will be.
Right now, I only need a little more than 120gb. Moving up to 240 or 256 would be plenty right now, and I wouldn't need a separate storage drive. This would also be cheaper than 2 drives. If I run out of room at 240, I can always upgrade at that point, when the cost for extra storage is even lower.
And since I already have external HDs and offsite backup plans, spending extra money for a dedicated internal HD only for backups is fooling money away.