My company has about a half-dozen heavy users and we spend more than $300 per month on this junk. A lighter-weight $20/month solution could do very well I think. Here would be my feature list:
* Cross-platform HTML5, not a java plugin or Flash
* Cope with multiple screens and very high screen resolutions for presenters (so viewers on crappy hardware don't suffer)
* Simple interface. Nothing but "share screen" and "invite participant." No chat, surveys, hand raising or other cruft.
You would also want to support corporate pricing as a lot of users are at big cos.