The Answer If your current website is one of the latest designs and features a responsive layout, it may be possible to add an ecommerce section. If it is one of the older designs (Non Responsive) I.E not mobile friendly, then it is not worth doing. But we could add what you have now to a responsive layout for you.
These are a bit harder to upgrade, but adding a plug-in from the likes of PayPal can do it. This will not give you the full control of your stocks, discounts and invoicing, but works well enough for you to add a shop to your current website at low cost.
You get the full shopping cart with all products with each item priced and the ability to ad multiple quantities and items. Once the customer makes their choices and presses the checkout button, your site then goes over to PayPal for them to take the order and payment. PayPal will then email you with the order, putting the payment taken into your account with them.
You will need an account with PayPal and to remember that it’s not free, they will take a percentage of the transaction as their fee. So when setting up the account, please ask about fees. You will also find transaction fees and other costs come with all on-line payment gateways.