Theses guys make nothing ,the tip is for a safe drive and grabbing our heavy ass bags . They live on tips , a different job than you ,First officers usually tip a buck or two depending how far the ride is , local airport hotel a buck. I tip 2-3 , holidays Christmas I’ll give him $5. Grabbing those bags of your take there toll on their bodies also.
If it’s not a safe ride or damage your bags that’s different . If you really cannot afford it (really) then don’t or if your just being really really cheap well you have to live with your self.