Buying multiple gig quantity

[anukritikandpal]

I have a gig of $10 that I deliver in 2 days. I deliver the video in 1 day for $5 extra. But when the buyer purchases multiple gigs, for example 3, and add fast delivery, it costs  them $35 Instead of it costing them $45. Why is it so F'd Up? Now I am suppose to edit 3 videos in a day for just $5 extra??

And even if the buyer does not purchase extra fast delivery and they add 20 gigs while purchasing (thats the max they can do), so that has to be delivered in 2 days?

Is there a way around it?