I would like an ecommerce site - how much would this be on a monthly pay as you go?

You need the core system at £15.00 per month + the Ecommerce add-on for £10.00 per month - making a total of £25.00 per month.

This will give you all the tools you need to get your products online and if you need extra functionality at a later date, you can upgrade with more add-ons.