There's a big difference between "should" and what JR allows to happen as you know.
From what you mentioned previously, I thought you said we were around 61m currently IIRC, so if you add 17m for Murakami and 4.5m for the reliever we just added, we're already around 82-83m, so as you can see we are already getting close to your 90m budget number without addressing SP at all or the BP further.
If they move Robert for Petty and eat say 8m of the 20m, we have hit two birds with one stone by going down to around 70m and adding a cash cheap SP with still significant ammo to land another SP and maybe have room for the Houston CF salary if they trade Cannon for him.