The best way is to ask around. Search for local web desginers and then follow up on their references. Find local web sites that you like and find out who designed them.

Although PHP and MySQL can each be used independently, their combination opens up a new world of dynamic possibilities for a web site. PHP and MySQL compliment each other to achieve what neither can do alone. PHP may be used to gather and process data. MySQL, in turn, is used to store the resulting data. PHP may be used to retrieve and perform complex computations on previously stored MySQL data, combine it with other data and then render the results to a user’s web browser in an easy to read and useful format.

As the Internet matures and web users become more sophisticated, it becomes increasingly important to deliver more dynamic content and to offer more interactivity to fulfill the "instant gratification" demands of today’s web users.

This is the million dollar question. There is no simple answer. Basically, you get what you pay for. At least, as long as you're dealing with a reputable web designer.