Hey PR,
If it is just the zip it can be repaired by any tailor(get yellow pages and call around them you want a zipper replaced, If they say "Harro" get ready for ur nuts to be squeezed...should only cost you $20-$30 tops). Just make sure they use Polyester/Nylon Thread and it is spaced the same as your other stitching on the wettie(if the stitches are too close it will rip right thru...also if they use cotton thread it will rot) Also you can get a zip from Lincraft or Spotlight. YKK produce the best zips. You will be looking for a 10mm wide and maybe 55cm long?(measure your existing one...Plastic/Nylon teeth)
If you have major probs let me know im sure I can locate your size zipper in Sydney.
Good Luck