Hi @joslud

You should calculate an interest rate of at least 14% APR (1 year)
Below 14%, it is difficult that anyone will rent out Steem Power
The higher the APR you want to give in interest, the easier it is for someone to delegate to you.

Example
You can do the math like this:
Rent 1000 SP x 14.60% = 146 Steem
146 Steem : 12 months = 12 steem

So the rental price for 1000 Steem Power is then 12 steem for a month (that is, 4 weeks)

But it is the market that determines prices