need help fine tuning already working rewite for ssl

[onejz]

hi, i need some help fine tuning rewrite for my ssl. what i have now has everything going to

http://www.site.com/members

rewritten

https://www.site.com/members

but the problem is ssl takes a toll on site performance. i need to set it so that only /members/login /members/account and /purchase get rewritten https, which will be easy enough. but i need everything that isn't those two to be http, and the problem is once the url goes https, its staying https for everything. does anybody have any help on how i can tune the following rules so that after users are done on the three that i am going to send them to on https, i can get the url rewritten back to http.

with these rules, it rewrites from https to http when going from /member/login to /member, and then rewrites to https when going to /purchase and /member/account, but then doesn't rewrite back to http after; only /member/signup to /member rewrites back. any suggestions?

RewriteCond %{HTTP_HOST} ^site.com$ [NC]
RewriteRule ^(.*)$

http://www.site.com$1

[R=301,L]

RewriteCond %{SERVER_PORT} !^443$
RewriteRule ^/member(.*)$

https://www.site.com.com/member$1

[L,R]
RewriteCond %{SERVER_PORT} !^443$
RewriteRule ^/purchase(.*)$

https://www.site.com.com/purchase$1

[L,R]
RewriteCond %{SERVER_PORT} !^443$
RewriteRule ^/member/account(.*)$

https://www.site.com.com/member/account$1

[L,R]