sounds like you would like to develop from scratch your own code? or are you asking for our experience with any php-based open source auction pakages?
if you are wondering why php would be good to develop from scrath here you go:
php is free, so it will only cost time to implement. But as a developer time is money. If you are more comfortable developing in another language that might be quicker only because you know it better.
state of the art interface
you will be restricted by web-browsers for this. There are packages that help you write complient code. PHP comes integrated with the WebServices buzzword, ala XMLRPC and SOAP packages, so any code you deploy on a webserver can be hooked up to any other interface you write for any other platform, and long as it talks SOAP also. You could write a nice looking VB script to manage the auction for instance.
Fully enhanceable for future development
PHP will be long lived and allows object oriented code and php5 allows development using Interfaces (ala java) so you can use any oo techniques and stategies you have developed elsewhere for project management
Easy to modify for a programmer such as:
Amending & including different auction formats,
allow total freedom to designing the html output (front end)
php has access to many templating interfaces, as well as xslt tranformations. So you can either have a template engine write you html, or use your own xml transformations to generate your front end, seperating data from display.
adding additional functions & services
you can break up your php code into libraries, and oo inheritance should provide all you would need to expand your code.
Be License free once the software is established
php itself comes with no restrictions on licensing code written with it, unless you intend to distribute a modified version of php itself with your code
hope this helps get you thinking
