Air conditioner unit prices vary widely based on the type and BTU rating. As of 2015, prices at HomeDepot.com range from $115 for the least expensive window unit to $5,054 for a built-in unit with a heater (prices do not include installation).
Portable air conditioners are also available and tend to be more expensive than window units but less expensive than built-in units. Frys.com sells portable units ranging from $299 to $479.
BTU ratings affect both the price and effectiveness of air conditioners, with higher ratings costing more and cooling more. For a 300-square-foot room, HomeDepot.com recommends an air conditioner with 10,000 BTUs. Prices for 10,000-BTU air conditioners on Walmart.com range from $249 to $599.