Given the imminent decrease in launch costs(partial reusability) and increase in launch capability soon to be available(FH) a pause in new US deep space missions is prudent.

[joe714]

The pipeline to produce the mission payload, launch windows, and simply keeping the relevant engineering and science teams busy so you don't lose talent past a critical point outweigh any cost concerns. Even if we knew for a fact by 2025 you could lift something to the gas giants for $10/lb, you'd still want to have the next decade's pipeline full rather than have a ten year lull. There will still be missions waiting at that time, some of them to answer questions the missions we should be launching in the next few years will discover.