I have to agree with Dick's and B Matthews last posts, the most bang for your buck is going to be to keeping the structure as lightweight as possible, while maintaining the strength.

And just to throw out another option rather than using a full scale aircraft is, if speed is not an issue what about a dirigible type of delta aircraft? With the need for high lift offset by by gas in internal bladders your AUW would not be as much of an issue. You may see now why balloons have been the staples of both weather and atmospheric research for years.

While the engineering challenges of such a project may be daunting, it is by no means impossible...