I have a different way for calculating it.
Let's have a nice round number, like 2 SBD for a post. If you choose 50%/50% you will get about half of that in SBD after a week (1 SBD) and a sixth of that in SP (0.33 SP).
If I use the current value where 1 SBD = 10 USD, then if you sell what you made from a 2 SBD post, you made 10 dollars from the SBD and 3.3 dollars from the SP. 13.3 USD in total.
You obviously need to remove whatever fees the conversion will cost. If you are lucky, it's 1% for converting it to another crypto (let's say Litecoin, as Bitcoin has way too high fees). You are down to 13.1 USD.
If you want to bank them in a physical bank, there is about 3$ fee for the transfer, so you are down to 10.1 USD.