I'd just set up a mixte as a touring bike. Mixtes are plenty strong if a tiny bit heavier than the equivalent double-triangle frame. Not so much the swoopy mixtes and the normal step-through frames; make sure the frame is a true mixte with the top tube/tubes running straight all the way from the head tube to the rear axle.
Setting up as a touring bike mostly requires strong wheels, appropriate gearing, rack mounts, good brakes and comfortable handlebar and seat. Soma has the Buena Vista for about $400 for the frameset. Origin 8 has a mixte frameset for half that. I tend to prefer mid-80's Japanese mixtes as they can be acquired for a hundred bux or so, and some of the components are good enough to re-use. Stay away from the French marques and early low-end Raleighs- they often have incompatible threading and diameters that make for a challenging upgrade to modern componentry.
Last edited by cycle_maven; 10-23-12 at 09:46 AM.