This is true historically, but costs are starting to be dominated by "picking up a big rectangle twice and screwing it down" or "finding someone with a flat surface that wants power and putting some stakes in the ground".

These will also come down. For example Fraunhofer is trialling a system where the panels come hinged and connected out of the factory and you just drag them out in a straight line onto the ground right out of the container. Also increasing panel efficiency means less handling per watt.

I'd expect the top end of the S curve to start becoming apparent at about 30c/watt for utility or $1/W for rooftop.