If-then-else mod_rewrite for Zend Framework and SSL in .htaccess

Question

I'm trying to automatically redirect for any url that has "checkout" in it to https. Otherwise, if the url is https but doesn't have "checkout", I want to redirect to "http:". Only urls with "checkout" can have https. I need an if-then-else structure. The syntax below doesn't work ... redirects to index.php if there is https in the url.

RewriteEngine On

RewriteCond %{HTTPS} !^on$
RewriteRule (checkout.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [R,L]

RewriteCond %{HTTPS} !^off$
RewriteRule !(checkout.*)$ http://%{HTTP_HOST}%{REQUEST_URI} [R,L]

RewriteRule !\.(js|ico|gif|jpg|png|css|swf|xml|avi|flv|mov|mp3|wav)$ index.php [L]