Over time, it will hopefully become clear what questions are actually worth. I would say I don’t recommend questions to be asked at the $4 rate unless they are absolutely beginner-level or unless the Asker is comfortable taking the chance on getting less-than-expert-quality answers. My guess is that questions below $15, say, will mostly be ignored by more experienced PHP developers.
In this scenario, it’s perfectly ok for Experts to comment and ask that Askers post the question again at a higher price, especially if the solution requires more than a couple minutes of figuring.
We are relying on the audience to communicate and participate more and make clear what their expectations are. As the FAQ page says, we don’t want anyone feeling they’re contributing time and effort to questions that aren’t worth the money. Experts should feel free to make polite suggestions if they feel questions aren’t being valued. We will monitor this over the next month or two and see how it goes.