My rule of thumb has always been if the ticket cost more than $300, then burn the miles.

Besides, considering your travel involves returning on a Sunday in the middle of Summer, your ticket will be a bargain if it costs less than $250 (at least to/from MSP).

I see that you're a Plat, why don't you book the ticket with miles and if you find a cheap ticket later, redeposit your miles then. Your redeposit fee is still waived even if the ticket is issued to a different person.