re: fair bartering.
Good points by Nikole and Edgar about the traffic/visibility issue. Free banner sounds nice but if there is no real sustainable traffic, then the point is moot. I imagine there has to be at least 50 unique visitors per day before the designer can expect to make one sale back within a 30 day period. Probably more than that as I`ve tried something similar where I have my company logo on a client site for 6 months now (she easily gets 30-50 uniques/day) and I`ve not seen a sale from it. But the client paid me upfront so I`m not complaining either.
A basic brochureware site (non-CMS) would probably take at least 15 hours b/w mockups, iterations, coding, and setup? Of course, it can be tougher to please a fellow creative professional as well. :)
My opinion is that since you seem confident that you are getting national brand recognition, it really makes sense to pay for this upfront.
In bartering, too many things can go wrong including the designer bailing out, the designer has poor design/development skills, etc... Remember, the only designers interested in this are the newbies and they tend to lack knowledge about web standards, coding, usability issues, etc...
And if the client shows any signs of nitpicking, then this starts to irritate a designer as s/he is doing this for free and morale starts to decrease to the point where designer may lack motivation to finish the project. Client has deadlines as to when this site needs to get up and stress starts to take over.
Next thing you know, another horrible barterting trade went awry and SUN decides to put this up as their lead story for their weekly bulletin :)