I think that giving up the draft pick to sign Lynn or Cobb (I'm not interested at all in Arrieta) is huge. It's not only giving up someone who would immediately slot in as an organizational top 20 prospect and be a potential top 100 prospect, but it's also giving up the flexibility of the slot amount - the same flexibility that was so key to the high-upside picks of the the Twins 2017 draft. So, given that...
Plan A: Sign Darvish. I would go as high as 6 years 150 million.Since there is no draft pick compensation and this is an opportunity to sign an "ace" without giving up top prospects, I would go this high. I feel like this could very realistically get it done.
Plan B: See if Lynn or Cobb would accept 4 years 60 million.Factoring in the draft pick compensation, that is the max I would go. And I don't think it's enough to get either of them.
Plan C: Try to trade for Archer without giving up Sano, Lewis, and both Romero and Gonsalves. This won't be enough to get Archer.
Plan D: Go after second and third-tier starting pitcher targets. Odorizzi, Straily, Corbin. Also inquire about some other names that we haven't heard much about but that could be acquired via trade - like Michael Fulmer and Danny Duffy. This trade would have to include not giving up any of the MLB core (Sano, Buxton, Kepler, Berrios, Mejia, Polanco, bullpen arms) Lewis, both Gonsalves and Romero, Javier, or high-upside 2017-draft guys like Rooker, Enlow, and Leach.
Plan E: Sign a 5th starter type via free agency. Let competition play out in Spring Training and hope the young guys can contribute big in 2018. Put plan in motion to really improve the rotation for 2019.