B2 is $5/TB/mo, so that's $60/year. I wrote this little program:

  c = 500
  i = 0
  while c >= 60:
      c -= 60
      c *= 1.07
      i += 1
  print 'broke', i

At a conservative 7% interest, $500 invested would pay for 11 years of B2 service and you'd have $39 left over. For the last 10 years, the S&P 500 has returned 16.29%. Using that number instead, you could pay for B2 service and after 50 years, you'd have $136K in the bank. Or, rsync.net could have it in their bank.

Personally, I'd never do a lifetime anything. I've seen too many things go bust to believe in a lifetime guarantee of any kind. These things aren't guaranteed for your lifetime, they're guaranteed for the company's lifetime.