I think it all depends on what you want from a bike, how much money you have and what parts you already have.
If:
i. you have little to no money, don't mind 26" wheels, buy an older mtb from craigslist, put slicks on, buy some racks/panniers and trekking bars and you're good to go (caveat here is that depending on your weight, you might have to make sure your load is spread front and back or invest in a 36h rear wheel with hub)
ii. if you really want a 700c wheelset, have little to no money, then bide your time on craigslist for a bargain 700c tourer (course, it might take you months or years to get that one perfect bike).
iii. if you really want a 700c wheelset, have quite a few parts and necessary tools lying around and have little to no money but expertise in building a bike, go for the Nashbar frame!
iv. if you have loads of money.... do what you want -go wild and buy a custom tourer!
I'm sure I missed some permutations there... but you should get the idea. Building up a bike is rarely cheap unless you have the know how, tools and most of the parts in your parts drawer. It does provide you with satisfaction, but it'll usually leave you with an empty wallet! (even if the frame is $5). Buying a complete bike at a good price from craigslist is usually the most cost effective way to go, particularly in the case of using an older mtb, putting slicks on and retaining the drivechain. To get a purpose built tourer off craigslist usually will take time and patience -ebay is a better bet, but then you most likely will have to incur the not insubstantial shipping costs.