Digital photo blues

I am currently struggling with what to do with all my digital photo files. I am certain that if I was shooting film I would not have near the number of photos, hence the title: Digital Photo Blues. My backup procedure has been as follows: 1) backup to internal HD, 2) backup to external HD for home, and 3) backup to portable drive for offsite storage.The problem now is that only my internal HD is capable of backing up my entire photo library. The external HD's that I was using are now too small.Do I upgrade to 1T drives for the external drives? Both external drive boxes have the IDE interface. So instead of just upgrading the HD's I need to get new SATA enclosures. This increases my overall costs and renders the existing boxes pretty much useless. And how long will the 1T drives last? At the rate I am going, maybe for 3 yrs. Then I will have to upgrade again. I've looked at storage devices like the Drobo, which would allow me to continue using some of my existing drives, but it doesn't solve the offsite storage dillema. If all my existing HD's were SATA drives, then Drobo would probably make the most sense. A Drobo loaded with four 1T drives would cost around $1000. That's a lot of money indeed. So for now, I have 1 backup onsite and no offsite backup. I don't feel good about it. What would you do?