I actually own this set. My sister bought it for me about 15 or so years ago in Austin, TX. I think she paid $15 for it back then, maybe even less. If I can find it I'll pull it out and post some pics. They're still unpainted.... I remember really liking them a lot.
The Columbus set is probably the rarest set I own, aside from Atlantic 1003 (Geronimo Apache):
http://www.plasticsoldierreview.com/Review.aspx?id=578
Weird thing is, my box actually has an extra sprue with four figures, two standing and firing, two kneeling and firing. Not sure if that was part of another set or what. All figs are molded in dark brown plastic.