I believe the cost is reasonable, keeping in mind that with this kind of stuff you largely get what you pay for.
The dial-up is going to slow things up considerably. I’ve only used ViaVideo over broadband at both ends, so I can’t speak to exactly how well it will work over a modem. Maybe worth a shot, though.
Also, MS has Netmeeting, free. All the major ISPs should have some form of them. A huge selection can be found at download.com, which is a free/shareware site.
One nice plus of Yahoo Messenger is that it works thru a firewall/NAT router. Netmeeting and others that conform to the video conf. standard are difficult to impossible to set up thru such a link.