Well it's usually not so much a question of price, but availability, and restrictions. Obviously it wouldn't be much of an issue for a simple biometric scanner, but when you get in the realm of cyberware detectors and such, a rating six is the equivilent of brand new mil-spec, which the military might be too keen to have readily available on the market. I usually keep low priced, high value items balanced with high restrictions, along with in game consequences if the characters go around buying up all sorts of restricted and forbidden gear. For example, lone star might come a calling, or Ares might "politely" inquire how the character is getting a hold of their corporate issue heavy weaponry.
You could consider all that justification, and it is. Most of the time with programs, scanners, medkits, and such I will go straight for the highest rating, but the idea is that your average joe non-megacorp won't.
