I struggled with this for a while, then I solved it!
<form action="https://www.paypal.com/cgi-bin/webscr" method="post">
<input type="hidden" name="cmd" value="_xclick">
<input type="hidden" name="business" value="YOUR_PAYPAL_EMAIL_ADDRESS">
<input type="hidden" name="on0" value="Customer Name">
<input type="hidden" name="on1" value="Customer Address">
Name:<br>
<input type="text" name="os0" /><br>
Address:<br>
<input type="text" name="os1" /><br>
Amount to pay (£):<br>
<input type="text" name="amount" />
<input type="hidden" name="item_name" value="Window Cleaning" />
<input type="hidden" name="no_shipping" value="0" />
<input type="hidden" name="no_note" value="1" />
<input type="hidden" name="currency_code" value="GBP" />
<br />
<input name="submit" type="submit" value="Pay Now" />
</form>
Obviously, change YOUR_PAYPAL_EMAIL_ADDRESS to your actual paypal email address!
You dont need to pay £20 a month, a standard paypal account is all you need.