Classified Software With Full Source Code

I am looking for a script for use on a classified website. The script must have full access to source code and be easily modified. It must take paypal payments, would prefer one that the layout can be easily amended as and when. similar ones are the pro editions of webClassifieds, geoclassified, almond classified i dont need it installing etc, but would need to see a front end and admin area if my budget range is too low for this, please advise and depending on what you are offering - i can revise my budget.