Culpepper was not an option. Minnesota wanted a 2nd round pick and there is no way that the Saints wouldve given up pick #34 for Culpep.
Like you said, they wanted Brees all along and got their man. If for some reason he didnt sign, they wouldve targeted McCown and probably drafted a Qb to compete. Also, rumors came out recently that Payton was after Romo, but I think that is just heresay.