Okay so it's the start of your turn, Wayfarer costs $6. There are no $7 cards on the board.

Play Develop, trash Wayfarer. I'm supposed to gain two cards "in either order". So it seems like I have two choices:

1. First, gain a card costing $1 less than Wayfarer—i.e., $5. (Wayfarer now costs $5 as well.) Next, gain a card costing one more than Wayfarer—i.e., $6.

OR

2. First, (try to) gain a card costing $1 more than Wayfarer—i.e., $7. No such card exists; the gain fails. (Wayfarer still costs $6). Now gain a card costing one less than Wayfarer—i.e., $5.

In other words, it seems like I can choose between gaining a $5 and a $6 or just gaining a $5.

Is this correct—do I actually have a choice? Or is one of these two scenarios actually mandatory?