If you have a throwaway white sheet in your linen closet, you have a free ghost.
If you have a thrift store nearby that sells linens, you have a very cheap ghost.
Using some string and a big-eye needle, hang the sheet at several points from a tree in your front yard. Drape it over a coat rack or standing lamp inside. Draw on some eyes to give it some extra character (and include a smile if your ghost is friendly). Glow-in-the-dark paint can be a nice touch here, especially if you'll be placing your ghosts outside.
If you want to go small, use tissues instead. A dozen tiny tissue-ghosts hanging from the ceiling or even from the front porch is a nice effect.
Or, go with another childhood fantasy -- be the house where she lives…