I recon a 2nd server locally is the way to go if: a) you don't trust anyone else with your data, and/or b) have a users which requires access to data at any time.
If none of those premises are required, off site is the way to go.
At that point you're in for either paying for a service or DIY/ putting the box in a coolio or equivalent. At that point, I believe the cheaper option in the longer run, is to buy the service. Plus, you wouldnt want anything else to do with that service, other than making sure it actually keeps backuping as intended. Additionally, once the first DIY-backupserver has "paid for itself" and has become obsolete, needing new hardware gives a new hefty hardware investment on your part. (I don't take into account that price per TB is getting cheaper by the year, since ideally, to some extent that would also trickle down to paid services as well as customer grade hardware off the shelf. yet the miles may vary.)
Cheers