From someone who works as a web developer full time, there's a lot of factors that contribute to an overall quote for E-Commerce websites. Is there a bespoke design? What platform are you going to use? Is there specific functionality that you require that can't be supported out of the box?
In my case, we work on a pre-built theme which myself and various developers manage and then the designers have full reign over the theme and can customise is bespoke to the clients needs. The pricing for this usually starts at the Â£600 mark but as previously mentioned it can be a lot, lot more than that. We've done quotes in excess of Â£7,000 upwards.
With regards to products, we tend to leave that in the clients hands unless they have products on an importable format like a spreadsheet etc which we can insert straight to a database and load images for. If this isn't the case they would have to pay a fee for the data admin side of things, again, depending on the volume determines the price of this.
We often say to our customers we'll host the website for them as our servers are configured specifically for certain platforms and we also perform backups frequently to maintain constant reliability.
If you're just starting out and wanting to make quick cash, I would get to grips with WordPress, throw WooCommerce on there and get a free Bootstrap WordPress WooCommerce theme and edit the styling to make it a little more unique for your client. I would recommend charging Â£300 or below if you're just starting out. Get your name out there, improve your designs and before you know it you'll have a nice portfolio of clients and you can build a small business up.