Nat Fraser has twice been found guilty of hiring a hitman to kill his estranged wife, but on December 19 he will again try to clear his name at the Court of Criminal Appeal.
Fraser has always maintained his innocence.
Arlene's family said it was "just ridiculous" Fraser is allowed to appeal again, as £700,000 has been paid out in legal aid since criminal proceedings started against him.
Stephen Gillies, who is married to Arlene's sister, Carol, said: "I imagine the whole of Scotland must be outraged at the amount of money spent on this."
Carol said whenever Fraser has launched an appeal it is "too much to bear" for her family.
Arlene, 33, waved goodbye to her children when she took them to school in New Elgin, Moray, on April 29, 1998, before vanishing.
Fraser was first convicted of his wife's murder in January 2003 and after appealing to the Court of Criminal Appeal in Edinburgh, it upheld his conviction.
He took his fight to the UK Supreme Court in London. The judges ruled he had suffered a miscarriage of justice, but at a trial in May this year, a jury at the High Court in Edinburgh found Fraser guilty.
He is serving a life sentence and cannot apply to be freed on parole for at least 17 years.