> Do these really work?

Seeing is believing. This looks to be a case of truth in advertising.

> Are there cheaper ways of creating the positions?

Lots of pillows?

Beanbag chair?

Arm of a chair/couch?

Foot of the bed w/no footboard?

Foam leg elevator available from health supply (drug)store. This is a wedge-shaped triangle designed to raise the legs while in bed. Could be used for elevating other parts of the anatomy.