On average, Dodge Challenger spoilers cost between $100 and $250. However, if you want a really top of the line one made of carbon fiber or has backup camera compatibility, you can expect to pay between $400 and $800.
Whether or not you get a mechanic to put it on for you will also affect your bottom line. If you opt to have a mechanic install it, you can expect to add $100. Many spoilers some pre-painted, but in case yours does not, painting it will cost another $150 on top of that.