Can't speak to cost without knowing the layout of the system, but I would definitely cut and cap the line BEFORE it goes under the patio. Your instincts on #2 are correct.

@Revolutionary Gardens Thanks for your message. When you say cut & cap before it goes under the patio, do you mean cut off the sprinkler pipe completely so that no pipe goes under the patio at all or something still goes under the patio? I apologize if it's a silly question but a newbie here trying to navigate a patio project!

Depends. You want your paver base to be on undisturbed soil, so if the pipe is at a depth that can sit under the base, and it's not a brand new system, I'd leave it in place. PVC isn't going to biodegrade any time soon.

Of course, if the patio company is planning on excavating with a big machine they'll likely rip it all out whether they plan to or not. So that's a them decision. Hope that helps!

Considering the same. Addy, what did you decide to do?