Customer Portal

Not sure where to post this - just getting started with my site. I have read alot in the BH SEO forum. I just need to finish my site first. In order to finish my site, I need a Customer Portal.
My products is in the apparel industry and I offer my own credit account for purchases.
I need a portal for my customers to sign into to view their account information, make payments, view credit limits etc.

I have searched the entire web for a customizable plug and play type service but it doesn't appear to exist. Can anyone recommend someone to build this portal for me - or does anyone know if a software exists that I can simply purchase or sign up for.

Lots of portals exist for tech support etc but nothing that is applicable to the credit industry.

Thanks

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