Simple "Nike" costume
For dress-use a simple lace dress or cut a neck hole in a sheet to make a bedsheet-ghost style dress
for crown-take 2 leafy branches from a tree/bush. Tie into a ring with twine, then spraypaint gold
for shoes- Nike brand shoes or any sneakers
Optional- Put a large cardboard Nike logo on dress and/or the slogan "Just Do It"
I'll just post your suggestion, it's waaay too funny!