I think the bigger question you should be asking yourself is:
"How much paperwork do you want to create for yourself?"
By that I mean, The game is supposed to be fun and engaging.... and is at it's worst when you have to make a bunch of arbitrary dice rolls to check up on your equipment....
My major guess in the variance in weapon prices is (as said above) about quality. I am willing to bet that, the Krime Canon is a glorified POS, barely holding together.... But the ingram? A smooth sleek killing machine!
Now, in the interest of gameplay and mechanics, do you wish to complicate an already complex game with adding in a "quality" stat? And then what? roll each week to see if it fails? Each battle?
****
As a runner, you live or die by your Rep. You want a Rep of being reliable, non-talkative, easy to work with, and that you are a proven asset. Using basely held together crap gear does not inspire confidence in you, or your ability. In fact, it makes you appear "low rent".... and you don't hire low renters for high rise work.....