Is there someone who can share the cost with you? Dayti is right. There's no getting around fruit and nuts in a fruit cake. The mix will be the cheapest part of the cake and will likely not improve it at all.
From the OP, complication was first and cost was hidden in parentheses.
So, in short:
See if someone can share the cost with you and make it a group project.
Fruitcakes are easy. The list of ingredients is often long.
Decide now, so there are no hard feelings later. Non-cake people will have no idea how much money and time will be spent on this cake. The only people to whom I have given wedding cake have shopped for them first. They know what it costs retail and know the gift that they are receiving.
This small decision now will save you lots of grief later.