Why forever is almost free: details
Even if you want to preserve your data just over your lifetime, saving them forever is an added bonus at a negligible cost.
If it costs $0.01 per year to preserve 1 MB of data, the initial investment required to cover the costs for 60 years is $0.19 (present value of a $0.01 annuity over 60 years with an annual discount rate of five percent). Keeping the same data forever requires a one-time investment of $0.20 (since $0.20 invested at five percent will yield an annual investment income of $0.01), or only 1 cent more!
The actual calculations are a bit more complex since we take into account inflation of various costs, but the message is still the same: Paying an extra $0.01 per MB ensures that your valuable memories are preserved not only over your lifetime, but forever.