A FlyerTalk Posting Legend
Join Date: Sep 2009
Location: Minneapolis: DL DM charter 2.3MM
Programs: A3*Gold, SPG Plat, HyattDiamond, MarriottPP, LHW exAccess, ICI, Raffles Amb, NW PE MM, TWA Gold MM
Posts: 100,462
As a general rule, you don't want to be purchasing (for money) one way TATL tickets from a major legacy carrier. They're horrendously expensive. For one ways, you should either get award tickets or look for some sort of deal from a discount carrier (which is likely to be inconvenient and painful for a TATL flight).
Similarly, to upgrade TATL flights with DL miles requires purchase of at least an M fare which is about $4000 RT MSP-Europe and return.
BTW, this trip would be after gruaduation, right, rather than at the end of your son's final semester in college. Would you return to MSP after the trip, perhaps to pack up his apartment and move out then? Or do you plan to pack and ship (or even stuff it into the trunk of your car???) his stuff before the trip and then fly directly home from Europe? Where is home for you? Have you thought about how you would get to/from MSP from your home? If you plan to drive, where would you park during this period?