How much is a ticket from Madrid to Porto?

The cheapest price found today is $19.

When is it cheaper to fly?

Cheapest month is September — from $19.

Cheapest today — $19. Below is what booking services offer.

Departure	Airline	Stops	Price
Sep 23	Ryanair	direct	$19	View
Sep 30	Ryanair	direct	$21	View
Nov 2	Ryanair	direct	$26	View
Aug 26	Ryanair	direct	$27	View
Oct 1	Ryanair	direct	$28	View
Sep 9	Ryanair	direct	$30	View
Sep 28	Ryanair	direct	$33	View
Oct 24	Ryanair	direct	$33	View
Sep 29	Ryanair	direct	$34	View
Aug 25	Ryanair	direct	$34	View

How much is a ticket from Madrid to Porto?: The cheapest price found today is $19.
When is it cheaper to fly?: Cheapest month is September — from $19.

Links to booking services are affiliate links. The price stays the same for you.