Costs vary dramatically area to area and include supplier costs plus shiping, overhead of the clinic etc. This site goes over the use of it including dose amounts based on species as you scroll down
http://www.petplace.com/drug-library/xylazine-rompun/page1.aspx
You would need exactly what 'medium' means to figure out amounts to use.
But for costs those would vary by supplier for each vial.
Hope this helps you!
Cat Health, Behavior, Care Expert
30+ years cat owner, rescue, breeding, study of behavior & health care