I have a Soma Double Cross DC that I would tour on, if I had the chance. It could be built easily within your budget, I think the frame retails @ around $400. It's an excellent ride. Very buttery! It has rack braze ons, as well as disc brakes (the non-disc brake version is even less).
I feel like I'm constantly recommending this bike. I seriously love it.
'02 Eddy Merckx Fuga, Selle An Atomica
'85 Eddy Merckx Professional, Selle An Atomica
'10 Soma Double Cross DC, Selle An Atomica
Slacker on wheels.