I’m going to assume you are worried about the cost of additional bandwidth, and when it comes to bandwidth money can fix everything.
I think some of the participating affiliate programs might be willing to lend a hand. Surely the cost of helping to run this service is far less than the potential increase in sales from always having the latest promotion details available.
On the other hand, I don’t think many people would mind paying a small fee if you could save them a few hours of time every week.
Oh and yes, very good idea.