Maybe contact the creaters of DSD or KZK (can't remember full names) as they create avatars and then sell them using vendors (like vending machines) and when someone pays the machine it gives the payee a box which hey can open and it gives them all the items that make up the avatar or mod they wish.

Another way is to ask maybe a sim or person about putting up a vendor or small "box" this box could be like a poster that has physics and when someone pays it it does the same as the vendor except it's just a prim box with a texture picture put onto it showing the product they are buying.

I'm not good in the creation/selling industry of Second Life but I have done alot of shopping, if needs be, I could help you out by being a tester for you on things.