I'm new to the forum, but and building a new house and engaged an architect.
The problem I have found currently, and in the past is that there can be a disconnect between what an architect thinks it will cost, and your clients expectations are and what the builder can build it for. The architect designed to my budget, but he calculated at $16K per square for double storey inner city melb (thinking he would get the job to also arrange builder, etc). The builder looked at it, and has costed it at $12k per square. So now I find I can afford a bigger house, and have wasted 6 months in design and planning submission.
My next approach is a designer / draftsman the builder has worked with, his cost is $4000 through to planning ($2000 phase 1), cheaper than the architect, and the designer and builder seem to use the same budgetting model and costs. Architects WANT to organize the builder and they take a % of the total build job. Designers / draftsman seem to focus on making their money on the design work, not the build work.
I would recommend that you let the client engage a draftsman that you have worked with / built designs for, so that there is a mutual incentive, draftsman to be within your costing so that he gets more work from you, and early in the phase so that the set backs, heights, neighbours windows,etc or you might set the clients expectations too high.