I found this Human Ghost Display by Grandin Road via Scary Jane, who was righteously outraged that: 1) Standing a mere 5 feet tall, they’re only suitable for scaring very short people, and 2) Despite all of the photos implying that they’re sold as a group of 3, they’re actually sold individually…for $129. Oh my stars and garters.
A foam wig head, bolt of cheesecloth, and some glue will run you about $15. You could make a whole army of these for less than a single pre-made one. The method could hardly be simpler: Tie long strips of cheesecloth around the neck of the dummy head, layering them to make the body. Paint white glue–liquid starch would probably work too–all over the dummy head, then press another big piece of cheesecloth into the glue; make sure the piece that covers the head is long enough to also cover the neck and hide the attachment point of the cheesecloth strips. Let dry. Boom. Done.
These would be really lightweight, so you could simply hang them from the ceiling using invisible monofilament fishing line. You could also drape them over hat racks, floor lamps, or other tall skinny furniture to loom over your guests.
If you want transparent ghosts instead, you can make good-looking ones using packing tape. The basic method involves wrapping transparent packing tape and/or plastic wrap around a human form (a wig head and dressmaker’s dummy if you have them, a willing assistant if you don’t), carefully cutting a slit up the back to release the mold/person, then taping back over the cut. With several layers of tape the resulting ghost is sturdy enough to stand on its own, and is also light enough to hang just about anywhere.
Googling “packing tape ghost” will turn up loads of tutorials; there are some good ones at The Crafty Geek, Bandit, John Rozum, and Tape Sculpture (which also has a gallery of examples). There are also a couple of Pinterest posts (with no instructions) for visual inspiration: I like these spooky ladies in dresses floating around a tree, and this great-looking ghost made from a combination of packing tape and cheesecloth.
Somewhat related is this Instructable for Ghost Shoes, which includes solar-powered lights so they glow at night. Their method involves hacking cheap solar-powered garden lights for components; you could also save yourself a couple of steps and just buy the solar circuit and LED (in whatever color you like) from someplace like Evil Mad Scientist (who also has a tutorial for making simple solar circuits).
A fun yard decoration would be to make individual packing-tape ghosts of each family member (and the pets, if they’ll hold still [they probably won't hold still]) and then pose them in a tableau. Whatever you do, I bet it’ll be cheaper than $129.