I don't know.
Why would it cost more for a lesser availability item (18) on top of the added Karma Cost (x2)
I think the 30% is Pre & Post Chargen.
That is probably why it was listed AFTER both were spoken about.
If they listed it before (in the middle), then it might be taken as being only applied to Chargen.
Bad wording if you ask me.
It should read "Either way, they have to pay an extra 30% for the item"
After all, a good enough fixer can get Avail-18 w/o having to take any 20 Karma Qualities for it.