Re: the topic of this thread, I figured out a workaround that results in being charged the discounted rate for private registration when you renew.
This procedure works best for domains that are up for renewal imminently.
How to do it:
1) Cancel your private registration (temporarily) for the domain that you wish to renew. This will cause you to lose any remaining private registration service for the balance of the current term of the domain registration. (that is why it's best to do this when a domain is about to expire.)
2) Your domain should now say "public" in the Godaddy domain window.
3) Now go through the renewal process, and choose "private registration". You can select as many years as you want. The fee added for private registration will be $1.95/year.
The disadvantages are:
1) It requires timing the transaction close to the expiration of the domain, unless you don't mind losing a large balance paid for private registration.
2) It leaves a short window of time in which you are listed publicly. I went through this last night for one expiring domain and the time between canceling private reg. and renewing with new private reg. was about 10 minutes, but it let me do it. (I have no idea if anything on the web is likely to capture this info.)
The bottom line is that if you renew a (current) private domain through GoDaddy, the per year charge for private registration is $8.95 (more than the domain.) If you ADD private registration to a now public domain, the charge per year for private reg is $1.95.