So, this is rather unlikely but I had an interesting thought. If we presume the cubs aren't in on harper to the level we would expect because they intend to stay under $246 mil rather than them just not having money there is I believe a novel way around this. From my understanding the luxury tax counts as a percentage of games. That is to say if a guy is making say $10 mil and you acquire him after 2 months of the 5 month season you would only count 60% of his salary toward your luxury tax figure. I'm not 100% sure that is accurate but it seems to be.
If that is the case, what's to stop Harper sitting out until june or july? The money seems fine for the cubs after 2019. It seems like it's just a case of 2019 being the road block presumably because of the luxury tax. The other interesting thing is if he does sit out until after the june draft the QO pick tied to him goes away. And the other bit of interesting wiggle room from a cubs perspective is typically you keep some money until june/july for in season moves. So, that would in theory be money they have now but would typically be unwilling to spend because you never know what could happen by july. But if Harper were sitting there a FA in july.... it would effectively be like trading for a big player.