In my case OTHER NE features would be more desirable as add-ons than hot backup; with the relatively small installation we run, a cold backup only takes the system down for <10 minutes during a slow off-time period. Outlook Connector and/or mobile features would be more likely to get our limited IT $$ if they were available a-la-carte (but I have been on that one before and am not trying to beat a dead horse!)
But to your questions:
1. How many users do you have on your Zimbra server? 35
2. Region? Americas - U.S.
3. OS? Ubuntu
4. How important is support? For FOSS, forum-based support is sufficient, and better than paid support in some other products I could name!

5. Would you consider licensing Zimbra Network Edition instead? Probably not at our size. In a larger enterprise with a real I.T. budget it'd be a no-brainer
I would say that at the small-business size, a price of around $150 would be about right. I disagree with those who say it shouldn't be correlated to user base, as the larger number of users, the more clear the ROI for hot backup (and mailbox-based backup/restore) would become. I think a price of somewhere around (#users X $5 to $10) for an installation and upgrades for 2 years (renewable at an equivalent price) would be a reasonable figure.
Dan