I strongly recommend the 2010 Kona Sutra. I posted a detailed review of it here: http://www.bikeforums.net/showthread.php?593959

I love mine for commuting and I ride with two fully loaded Axiom Typhoons (large, waterproof bags) on the back. The bike comes with racks and fenders as well, ready to ride.

Regarding the Raleigh Sojourn, it's a nice bike, but for the same price the Sutra (2010 models anyway), the brakes and wheels are not as good, and I wasn't impressed with the quality of the frame welds either. You're really paying a premium for the Brooks Saddle and tape.

However, neither bike can be done "on the cheap" as its hard to find just the frames. Having a dedicated commuting/touring bike and a separate road bike is really the way to go, but it's not as affordable as just having one all-rounder. If you're just looking for a frame, you're going to have a tougher time finding something that meets all of your requirements, but you might look into the Salsa Fargo, which can be had for about $500 for a frame and fork. If you're really cheap, just get a disc fork (Salsa Fargo 29"/700c would probably work) and put it on your current road bike. With a disc specific hub and wheel, and a BB7 caliper, you can probably do the front disc brake conversion for about $250 if you're a careful shopper.

The most important thing to keep in mind when putting racks on a disc-equipped bike is the position of the rear brake caliper. It has to be between the two stays, and not on top of the seat stay, for you to easily mount racks. You can work around it (Kona did with the earlier Sutras) but everything is a lot easier if the caliper is between the stays.

EDIT: By the way, buying a complete bike would still be cheaper than buying the $1,175 Gunnar frame and fork + Avid BB7's + Rotors + Disc-specific wheels! For as much as you'd spend on the Gunnar frame alone, you could buy a Kona Sutra