Is it possible to use authorize.net's FREE Secure Order page, so I don't have to buy a secure certificate for my site?
So you want uShop set up on your Public (http) server.... and then want to use Authorize.Net's secure server to collect the payment information?
Yes, you can do that. Just install uShop as normal on your Public server. When it comes time for the customer to enter the credit card information, they will be transferred to Authorize.Net's secure server.
When I click "Continue" on the display_cart.html page it trys to connect to a https server on my site. I have changed the https://www.mysite... to http://www.mysite... in the setup file, as suggested in the instructions.
The "Continue" button on the "display_cart.html" page will link to whatever URL you specified as the "script_url" parameter of your uShopOrderButton applet. So on your "Place Order" page... make sure the "script_url" parameter of your uShopOrderButton applet is set to the "http" url. (You may have to exit/restart your browser for the changes to take effect.)
That fixed it.