Question

Are there any free ready solutions for a simple one-page ecommerce site selling only one product?
Like this one: http://www.brown-leather-belts.co.uk

Updated:
I don’t want to use any third-party checkout systems like paypal or google. My customers will pay cash on delivery. So I just want to receive e-mail with customer’s credentials.

Answer 1

The one mentioned in your post has done as little as possible and there is no need to add any heavy duty e-commerce platform/framework until unless you really want to have a full e-commerce portal.

The example has been created by just making a simple HTML form with one product and they have integrated it with pay-pal to payment option, when you want your user to go to payment gateway (paypal in the example), all you need to pass certain parameters (hidden form fields) to the payment gateway to work perfectly.Here are what has been used in the your mention use-case

<form name="_xclick" action="https://www.paypal.com/us/cgi-bin/webscr" method="post">
  <input type="hidden" name="cmd" value="_xclick" />
  <input type="hidden" name="business" value="[e-mail]" />
  <input type="hidden" name="currency_code" value="GBP" />
  <input type="hidden" name="item_name" value="The Broadway Leather Belt" />
  <input type="hidden" name="amount" value="60.00" />
  <input type="hidden" value="http://www.timhardy.com/thankyou.php" name="return" />
  <input id="qty-required" type="hidden" name="on1" maxlength="2" value="1" />
   // some other data not hidden fields
</form>

This is pretty standard way to communicate with payment gateway and you can find more information about structuring your form by referring the documentation of your payment provider.
For your use-case this is all you have to do

Hope this will help you