If you have a mage who has enough karma to easily get all of the stuff that he wants, then you're paying out way too much karma. Mages are karma sinks. This is not a good thing. This severely limits them. In fact, it is the one huge limit to the unbounded progression of the Magic stat.
And lets not forget quickening, and foci, and anchors, and all of those fun little extra karma sinks.
Mundanes can branch out, improve a variety of skills and stats, and become well-rounded characters. Mages have to focus almost exclusively on magical things or else risk getting left behind.
It is far far easier to improve with money than it is to improve with karma, which is why so many mages to sacrifice essence for some very important and useful pieces of cyberware.
If you have mundane characters who can't afford any upgrades, then you aren't paying them enough. Cyberware isn't cheap, but it isn't expensive, either, it certainly isn't as expensive as initiation. More importantly, equipment comes in boxes. Things that come in boxes can be stolen. Initiation is a metaphysical experience. You can't steal metaphysical experiences.
If a character with very little money wants a piece of cyberware, he can loot it. At the very least, he can cut the cyberware out of his opposition. Cutting useful cyberware out of dead bodies is a very popular pastime for shadowrunners.
You can't cut an initiation out of an enemy's dead body.
There are plenty of opportunities to make money, from organlegging to looting, PCs can potentially make a great deal of money off of even a low-paying run.
If they aren't taking advantage of this, it isn't the fault of game balance. It is the fault of the players. If they buy stuff that could easily be stolen, it isn't the fault of game balance, it is the fault of the players.
Spending precious karma on gear is the worst thing a mundane can do. He should be using it to upgrade skills and to make pacts with Free Spirits.