You're living in a HN bubble if you seriously think no new projects are being created in PHP, or if you think there are no valid use cases for PHP in modern applications.

Simply take a look at popular job sites - you don't even have to look at Monster.

PHP devs may be the cheapest as a whole because there's so many. If you're dead-set on finding a Go programmer they will come at a cost because there's so few.

Once you get into the higher level of skill, though, it starts evening out. IIRC the average senior salary for Ruby/RoR devs is only ~$5,000 more than a PHP dev.