Noafolumna is probablythe only better player you quoted, and its close.
Feldt drops the ball a lot and is just a finisher really. Johnston, has been great lately, but is extremely small and would provide little value for us considering a huge prerequisite for a winger signing is being able to take tough hit ups to start off sets, which is probably the poorest part of Johnstons game. He also is another 'finisher' and doesn't create nearly as many chances as JAC, nor is he half as good as him in open space. JAC is also a lot better out of his teams own 20m line.
He would definitely provide value at 600-650k. Anything over I would have question marks. But for us, he would also solve a problem of a fullback replacement for Tom... something which has dismantled us for the better part of two seasons. JAC would probably be the best signing we could make of players on the current market (besides maybe B. Smith if he even is on the market).