From your own link,
Antivenom is not particularly expensive, but because it is highly specialized, it can be difficult to find. A dose of antivenom has a market price equal to half the market price of a dose of the poison in question, but it is treated as though its price were five times the market price of the poison for the purposes of determining its availability in any given settlement. Alternatively, if 1 or more doses of the poison in question can be provided, most alchemists will supply as much antivenom as they can produce from the doses for a fee of 10% of the market price of the poison.
(Antivenom description, emphasis mine)
So it costs half the given poison does, or a tenth if you already have the poison. Mundane crafting costs one-third the purchase price, so a sixth or a thirtieth if you already have the poison.
The cost of the poison itself, however, is going to be up to the GM in a large number of cases, because there are not any rules for determining it. I do not believe there is any CR-based formula as you recall; I have never heard of such a thing and the closest I could find was a homebrew effort.