An excerpt about different costs of a placebo:

Dan Ariely, a behavioral economist at Duke University in North Carolina, and colleagues at the Massachusetts Institute of Technology tested 82 volunteers.
All got a light electric shock and were offered what they were told was a painkiller.
Half were given a brochure describing the pill as a newly approved painkiller that cost $2.50 per dose and half were given a brochure describing it as marked down to 10 cents.
Writing in a letter to the Journal of the American Medical Association, Ariely and colleagues said the effects were unexpectedly strong.
Eighty-five percent of volunteers who thought they were getting a $2.50 pill said they felt less pain after taking it, compared with 61 percent of those who thought they were getting a discounted drug.
The results fit with other studies that show charging more for something makes people value it more. But Ariely said the combination with the placebo effect was especially interesting.