I think that is too much for a rental too, but that's also why I think a Randolph or Moniak could be included.
For me his value is one top prospect, one guy with value, throw in a third piece because you are also acquiring the "recruiting period." I would not make any real effort to outbid the Cubs or any other team that is much further along in its growth, with more legitimate World Series goals this season. Not when you can just sign Machado this off-season.
And I'm not worried about that because I think this front office already knows they can get him. There is nothing unattractive about the Phillies - they have talent, money, and a deep history with him. If they are trying to trade for him in July that also means they're in the playoffs (as they would be if the season ended today). The market should also appeal to him - if he wants to keep it low-key he can and if he wants big-city stuff he can get that too.
The other reason to wait is you can then figure out what do with the four infielders after you've already got Crawford signed. Trade for a pitcher or re-stock the farm.
They gotta keep an eye on Machado obviously but I'll be surprised if they go get him. Stick with the team that's already winning, hope Hoskins and several others keep improving, add a pitcher if need be.