ToHo, you don't have to make the entire run the full-sized conductors. The trick to doing the voltage-drop figuring is to work from the end back toward the source.
Figure the voltage drop one load at a time. In other words, keep in mind that the last run only carries 100 watts, the next-to-last run 200, etc. Step up in wire size only when you need to.
I agree completely with Winnies suggestion of a multi-wire circuit, alternating hots. If the customer wants the recetacle always-hot, run a separate circuit, and use a GFCI receptacle, not breaker.
