This post reads like it's addressed to dthadmin, but as I'm killing time I thought I'd opine some stuff...
Sounds like we're talking about two different tiers of products. Tiers might be the wrong word, but basically two different products lines. One product line is for the live $4.95 webinars, and the other is for the archived $2 webinars.
The live stuff setup should be ready to go as-is. Nothing out of the ordinary for setup there.
The archived stuff *could* be setup ahead of time by creating a page/article where the archive's URL will be added to later (or added to at time of creation then delaying the "Registration Open Date" until after the Live webinar is scheduled to end).
For controlling how often/who accesses the archived shows a couple of ideas come to mind:
1) Restrict by IP address.
2) Make the archived registration page "private" which will require a valid login to get into it. Of course this doesn't totally lock things down, but it's a good start. You'll likely be able to record what username accessed it and probably an IP address can be captured via weblogs. The question then becomes, "with a little scripting, can you set up a process by which the script executes once an hour checking for webinar access by registered usernames, then removes that username's ability to access the URL again?"
Hmm, after pausing to think more about it, DT Register just doesn't seem to have that type of functionality built-in at present. Perhaps it will in the (near?) future. Until then, this product looks closest to what you're looking for (from what I can tell):
http://extensions.joomla.org/extensions ... ions/13345
-soccerbum