They're providing you a service by coding it up, hosting it, dealing with customer service requests and Southwest's lawyers, etc. Seems fair to charge $3 to provide the service of saving you money. Also seems fair to try outcompeting them by providing that service for free at your own expense.
Honestly, I think it's pretty lame trying to profit from arbitrage on SW prices like that. $3 per alert? Really?
Great job making an OSS implementation.