Ebay has new Hitron 4x6 sold by sonicelectronix for $13/pair with free shipping, and various sellers have Pulsar, Boss, Pyramid, Legacy,... for $18/pair shipped.
The 4x6 speaker size isn't the epitome for sound so no point in spending a ton.
There is a pair of NOS Boston Acoustics S75 for start bid of $40 and a good selection of Polk, RockfordFosgates, Alpine, JBL,... <$60, and JVC, MA Audio, Planet Audio, Lanzar, Kicker, Crunch, Pioneer, Kenwood, Pyle... <$40 pair delivered.