Ah!
Well, you can begin with simple tutorials on using a money-based system, which can be simple PHP with a database (MySQL for example) and using a shopping-cart mechanic to work it all, with the usual membership script.
PHP Coding Membership Scripts Tutorials
PHP Coding Shopping Carts Tutorials
Then, what I would do (if I were any good at Flash) is have a Flash application that pulls the stats from the database on a given member. It can retrieve the user's items, money, status, and whatever other stats it may need, and dynamically throws the items together. The method of putting those items together would have to be up to you of course, and you could probably make another table in the database of all the possible items, and what stacking order (or z-index) that particular item should have. The script could then match those variables together, and draft the character avatar.

Since I'm no good with Flash, I would have to use base files, having each item as a seperate image in folders, then using a loop and layering the images together.
If you're interested in the Flash route, you could dynamically create a class with each object that the script can draw in Flash, if you didn't want to have image files everywhere; would be more tedious, but still a possibility if needed. Either way, these functions may be of some use.
PHP: Shockwave Flash Functions
PHP: Image Functions
Hope that helps to put some outline on the sort of things involved.