The definition of "low-grade street muscle" is flexible and open to interpretation, but for the purposes of this reply I'll take it to mean a street ganger.
First, Jack_Spade is right that drugs are a great equalizer. Pump some goons full of combat drugs and they'll go from "not competitive" to "potentially dangerous", especially if there are a lot of them.
If you're talking about augmentations, I don't think it's unreasonable for a ganger to have some. Remember, you don't have to take nuyen too literally: not everything is paid for in cash. Think of it more as assets, or even opportunity cost. Even a ganger can repurpose a cyberlimb that fell off the back of the truck (or off the dude they beat the drek out of). Used augmentations are ideal for street scum, PC or NPC.
Acknowledging in advance that the sample characters in the core rulebooks are meant to be PCs rather than grist for the mill, they can still offer clues as to what's reasonable for a ganger to be running around with. Here are the augmentations from the sample ganger characters from SR3-5:
SR3: dermal plating R1, retractable handblade
SR4: muscle replacement R1, datajack
SR5: cyberarm (standard, used, obvious, with precisely zero enhancements or customization)
Taking a different approach, you can turn to the grunts at the back of SR5 (p. 389) and see that a ganger lieutenant has a retractable spur but the rank-and-file don't have anything.
I think Marcus' original list would work well for the leader of a mid-sized gang, especially if everything is used. Subtract 1 or 2 things for the lieutenants, depending on the gang's resources, and subtract another 1-2 things for the front line cannon fodder.
