I don't think the Raiders are ever a chance of signing somebody for small money. I seem to recall that Canberra almost always have to pay overs, largely because they need to pay an incentive to get people to actually live in Canberra (I'm not joking!). They almost solely rely on junior development and frankly I cannot remember them making any notable signings in recent times.
Their recruitment almost exclusively consists of rejects or journeymen (this year's signings include Lagi Setu and Kurt Baptiste) and other than Blake Ferguson I cannot remember them signing anyone in the prime of their careers in recent years. For them G-Stew is probably as good a signing as it gets.