The couple, who became engaged in November last year, are said to be planning a lavish marriage ceremony on the Hawaiian island of Kauai.
According to Cover Media, Simpson will fly around 50 family members and friends over for a week-long celebration.
Costs for the wedding, which Simpson is believed to be paying herself, are thought to have spiralled to around $1 million.
Simpson dated the American football player for around six months before becoming engaged, after the two were introduced by mutual friends.
The singer is organising the nuptials with celebrity planner Mindy Weiss, who also worked on Simpson's 2002 wedding to Nick Lachey.
Lachey, who was married to Simpson for three years, announced his engagement to Vanessa Minnillo only a week before Simpson revealed her own engagement.