what resins or epoxy are people using to re do the decks?

Depends on what you mean by re-decking. If you mean re-gripping, something UV stable. I use Barnes epoxy glass, after a good clean and dry. rolled on thin, then sprinkled evenly in caster sugar. It doesn't look anything like the original grip, but in my opinion its far superior, grip wise.

if you mean deck repair and you're going to paint it afterwards, any epoxy above bunnings grade. I use international (standard hardener) stick to standard hardener whatever youre doing, don't use a fast one, the heat will f**k things up

On the cheap? On the ugly? I just spray clear coat and blow over some non slip granules.

Nautix do a 2 pack grip product that works very well "nautix grip" - 1 pack would easily do 2 boards. Or you can just roll cheap epoxy onto the board, sprinkle with granulated sugar and off you go (until the UV turns it brown).