A lot depends on the business you're in. But most retail stores would be able to get a pretty decent, custom designed eCommerce system.
It could be either open source or proprietary software running the store. If it was me though, I'd spend max €6k (depending on the business of course) and spend the other €4k marketing the site (online).
You'd come out with a pretty decent solution that should easily generate a return on the investment.
