When it comes to PHP frameworks, my ideal choice is UIMS kit as mentioned here. UIMS, in my term is a webpage creation kit in which the client/end user can easily create the UI, forms, validations, etc by dragging and dropping (more like Delphi). Though I strongly believe that the future of web application development will totally be driven by UIMS, it needs time and effort to build the UIMS kit. In the meantime, any framework that is lightweight or feature rich is the economic option.
Some of the lightweight PHP frameworks: