Your air conditioner does not consume refrigerant — it is a sealed loop. So if the system is low, it is leaking, and the only real fix is to find and seal the leak, then recharge to the correct amount. Detecting the leak (with electronic sniffers, dye, or nitrogen pressure testing) typically costs $100 to $330; the full detect-repair-recharge job runs $200 to $1,600, around $800 on average, depending on where the leak is.
This is also the single most important consumer-protection point in AC repair. Under EPA Section 608, a technician may not simply 'top off' a leaking system — adding refrigerant that will only leak back out is illegal venting. The rule requires the leak to be repaired before new refrigerant is added, and violations carry penalties as high as $37,500 per day. An honest shop locates the leak, repairs it, recharges by weight, and bills you for the actual amount of refrigerant added.
The classic scam is the annual 'recharge': a tech adds a pound of refrigerant every summer and never mentions the leak, so you pay again and again while the problem worsens. If a provider offers to top off your refrigerant without testing for and fixing the leak — or if you have paid for refrigerant more than once — that is a red flag, not a service.