Can you refresh ONLY the wordpress adminbar and not the whole page?

I would approach that problem slightly differently.

The entire bar does not need to reload.
Instead it needs to stay “current”.

So to do that you load your initial value…let’s say $100.00

Then you use Javascript to see if new values have been added and then you update it client side.

You could even do a cool little fade out and fade in of the old vs new value.

Just have your script check every 60 seconds.

Example:
https://www.google.com/search?btnG=1&pws=0&q=google+stock

Just wait like 60 seconds and look at Google’s Stock numbers – they just update on their own.

Tutorial:
http://www.webdeveloper.com/forum/showthread.php?t=169337

Relevant documentation:

http://codex.wordpress.org/AJAX_in_Plugins

http://www.garyc40.com/2010/03/5-tips-for-using-ajax-in-wordpress/