According to the Hebrew, Saul took three eleph with him. Eleph could refer to a company/unit1 of men or to a thousand. Most likely, given what he knew of the men that David had with him (see 1 Samuel 25:13), he took at least two or three times that number to ensure that he had numerical superiority.2
2 So Saul arose and went down to the wilderness of Ziph with three thousand chosen men of Israel to seek David in the wilderness of Ziph.