But if the system you’ve built is of any complexity, you’ll inevitably pay for the learning curve that actually matters: absorbing the system’s architecture. Compared to it, the time it takes an experienced programmer to get up to speed with a new language isn’t very significant. (Admittedly, this thread is about a pretty simple system; though who knows where scope creep might take it (see my signature).)
Hiring a “PHP programmer” is mostly a way for a non-programming manager to find someone vaguely fitting, because he can’t effectively evaluate a programmer’s skills on much more than prior experience with particular technologies. But such a manager is in for a rough ride at the best of times, anyway.
I suppose “programmer with $FOO experience” makes it more palatable; but the core point remains the same.
Makeshifts last the longest.