Hello, I represent a team of designers and developers. I am sure my developers can make a script or simple software to update or post your craigslist's posts.
I think it is impossible to stop spam bothering you, because only website can control spammers (that is why, actually, they made additional internal email system).
Also when it is time to "renew" a post, it is better to post a new copy of your message. If you do so, you will get a new post posted today and an old post posted 15 days ago. This feature helps you to have more posts without getting a system message that you used all available messages.
For example: If I post resumes, I am limited to have only 4 active of them. With this feature I have much more working posts.
Price is a subject to negotiate.
Regards