Where are you? Those prices seem insanely cheap. My local dealer is at least 2k more than that on the grandee.
At those prices I would definately buy the grandee. The wood sturcture doesn't bother me; but having owned 2 hot tubs previously (15 years of ownership) the polymeric tub in the base of the highline and the ceramic filters you can clean in the dishwasher seem worthwhile upgrades...