So you play one highway without patron and one with patron, and then you wonder if cards can go below 1 or nor?
I'd say: last played card counts.
I'd say it's very clearly always $1. The Patroned Highway would read (other effects aside): "While this is in play, cards cannot cost less than $1". That is a clear instruction, and playing a normal Highway does not contradict it "Card cannot cost less than $0" is always fulfilled if cards cannot cost less than $1. The other Highway also cannot decrease the value of a card costing $1 since Patroned Highway says that's impossible.
By the way, I think Patron needs to specify how long the coin increase lasts. "Until that card leaves play" seems to work. Otherwise you could assume that the increase is permanent, which is untrackable. It would also have some unresolved issues with Reserves (can I or can I not use this to gain $7 cards with Duplicate?)
Fair explanation. I played Patron as if it said 'until that card leaves play', because it just felt obvious. Probably the maker should have included it. (It's not my card.)
Also: If I remember correctly, you don't *play* reserve cards, you *call* them. Patron specifies that you can only use it when a card is *played*, which is not the same, right?
I think you are right in the first explanation.
The question is: if I raise that coin, does that mean that curses and coppers now cost $1? I think they should, reading it as two separate clauses:
(1) All cards cost one less
(2) no card costs less than $0 (=> $1)
Another way of reading it would be
(1) all cards cost one less and (1B) this effect can not cause cards to cost less than $0 (=> $1)
the latter reading would imply that cards that already cost $0 do not need to be raised though.
What reading would you prefer?