We're a small Django shop and I do weigh up this when deciding if we're the best option for a prospective client. If we build them a site then there is a maintenance cost that is potentially higher than there would be with a PHP site.

Of course - the counter-argument is "a good PHP dev is no cheaper and just as hard to find" but for maintenance tasks you might only need an average (or even mediocre) dev - and it's a hell of a lot easier to find an average PHP dev than an average (insert less popular choice here) dev.