According to calculations I just did based on the Steem Dollar tool, as of 9/11/2016 at 1:00 am CST, the answer is 190.48 steem power equals $0.01 in upvote power.

Using the Steem Dollar tool; which can be found here (thank you @mauricemikkers for building this)

http://www.steemdollar.com

It calculates that when I am at 100% voting power, an upvote from me is currently worth $0.010263027107793.

<a href="https://www.steemimg.com/image/yy2gP"><img src="https://www.steemimg.com/images/2016/09/11/ScreenShot2016-09-11at1.01.52AM35786.png" alt="ScreenShot2016-09-11at1.01.52AM35786.png" border="0"></a>

I currently have 196.489 steem power, so that means I only need 96.94% of that for an exact $0.01 value increase… which is currently 190.48 steem power.

This is slightly changing/fluctuating constantly, and I’m interested to see how that calculation changes over time.  Also interested in seeing if this is actually accurate.  Today is my first day really digging into the Steemit platform and this is my first post -- so for all I know, the calculator I'm basing my findings on could be completely wrong, and I don't have enough experience to know firsthand if these numbers look right based on my account, yet.  Does this calculation + tool that I’m basing the calculation on seem to hold up for you?  Or did I just do some worthless spreadsheeting?  :)

Also: Thank you to @fabien for creating the Steem API that @mauricemikkers is using to power the Steem Dollar tool.