I have built several custom e-commerce systems in Perl myself, as well as worked some with pre-made options, including Interchange, Web+Shop and OScommerce (which I'm still evaluating). If you have generic needs and expect things to stay that way for the short term, I recommend looking at pre-made options.

Right now I'm impressed with OScommerce, although it is written in PHP and MySQL. I would recommend that you take a look at it as well.

If you really want to jump into rolling your own, you may want to contact this fellow from the CGI::Application list, who is also working on a new Perl-based. e-commerce system now.

I would be prepared to spend at least 30-50 hours of development time if you go this route.