Cuadrado could actually be a good player for us. He could add depth to both midfield and attack and can start in RB position too and maybe RWB. He will be a great squad addition. But he should not be our primary RB though.
I would go for gundagon, cuadrado and one defensive RB. Next season we could try for verratti. But for now gundagon or kovacic has to do, first one is easily the better fit and more experienced.
I suspect one of the main reasons why there are so few great RBs around is because most good players are moved by their coach to a more central position where they are more involved and influential in the team play, like Puyol was back in the day. They start out at RB early in their career but are then moved to central midfield or central defense. We see this again with a guy like Fabinho from Monaco. He plays well at RB and now the coach has moved him to central midfield.
An option for us could be Allan Loureiro from Udinese. He is played as CM or RWB, but has all the qualities of a Barca RB. Extremely fast, great tackler, great dribbler and superb work rate and stamina. He's at the right age (24) as well. I'd love to see Allan for us.