Seems like there's virtually no chance payroll goes down/stays the same in 2018 unless they unload guys.
According to Spotrac, they have about 73M tied up in 12 guaranteed contracts already. Plus at least 8 pre-arbitration guys on the 25-man next year making roughly 575K each, which puts them at about 77-78M
Picking up Brantley and Tomlin's options and declining Logan's is another 16M. If they keep all seven of the arbitration guys, that's another projected 34M.
So before you even get to the free agents, they already having about 127-128M in committed salary. If they keep Santana and Smith, you're talking right around 150M.
2017 payroll was 139M.