What are the best live webinar tools for small audiences (<500) and budgets?

You actually have many more choices in easy-to-use, low cost web conferencing platforms than you do at the upper end, but you shouldn't rule out WebEx or Adobe Connect without getting price quotes. They both offer various services and pricing structures, and it's likely that you could find something to suits your need.

But having said that, pricing usually goes up quite a bit based on room size (the size of the meetings you'll want to host). 500 people is considered a large room size. Pricing usually starts with a room size of 25 people and can go up to 500, 1,000, or more. If you're not sure how many people you're going to attract to your online meetings, then start out small. Most vendors are happy to increase your room size (and price) if you need it.

Something like Citrix GoToMeeting is probably your best choice for ease of use, well-rounded features, reliability, and pricing, but there are plenty of other options. You can find a good, vendor-neutral comparison of available services here: http://www.webconferencing-test.com/. One thing I always look for is stability--unexplained crashes during your meetings are no fun.

Before you start to gather quotes, I'd advise you to think through your plans and come up with an idea of what kind of experience you want to provide for your attendees. There are some really intriguing options out there, like ViVu, http://vivu.tv/vivuweb/. No one says that all online events have to be the same (desktop sharing, polling, Q&A, chat) or mimic in-person events, like some of the online conference services do. We're seeing a lot of growth in this area, and I think it can be driven by people with a vision of what they want their online events to be.