It is not about the cost, it is not about the value...
It is about the weirding ways...

The SBDs are yours to decide, the SP is for you to share ;)
Also the other two prices are convertible to rented SP.

Last time i checked was 200 SP per Steem per week so 4 weeks of 500 should amount to about 10 steem.

Maybe @reggaemuffing can shed some light?