I'll keep this simple. I'm GMing a new campaign, and want to make the whole thing more Cyberpunk-esque. In my game, magic is (at the start of the campaign) relatively unheard of, UGE is starting to appear, and Dragons are spoken of only in reference to obscure RPGs. Of course, I'm letting one PC start with magic, but being an adept, he does'nt actually know it. Cyberware is pretty rare; anything above Boosted Reflexes 1 is pretty rare, and BR is often only taken by gangers and other types that live on the edge. Deckers are common as heck, so the PCs can afford to hire some middle schooler script kiddie to get brain-fried for them. (Not to mention save the GM some effort.) Drugs and crime is everywhere, but true shadowrunners are very, very rare; the PC's are likely to just end up comitting petty crimes for cash until they build up a reputation.
Here's my ideas pertaining to character creation:
1. All players start with 300 karma. (BECKS rules; I may have misspelled that.)
2. Adepts and most Aspected Magicians start with a magic rating of 4, but a karma cost of only 40(Aspected Sorcerers must pay 50.) True Magicians have a starting Magic of 5, and a karma cost of 75.
3. Non-physical skills (Electronics, Etiquette, Pepperoni B/R) cost 1/2 normal.
4. Cyberware (and bio, if it can be afforded) must have surgery costs included in the price.
Sound fair?

No FFBA.

Golden Rule: Ask the players to create reasonable characters.

You'd be amazed at how well this "rule" works above all others, especially when playing with friends rather than strangers.

I'm not familiar with the BECKS system, so I can't give feedback on your numbers there.

1. A Magic Rating of 4 doesn't stop an adept from having 6 points of powers. Your game is not going to have any sammys, just adepts and people that suck ass.

2. Do not even bother trying to limit things based on availability, they're just numbers the developers pull out of their ass. Limit things by TYPE. If you want a true low-power game, just ban all automatic weapons besides machine pistols.

3. You have in no way limited what they can start with cyberware-wise beyond vague hand-waving that XYZ is "very rare". List EXPLICITLY what they can and cannot start with when it comes to cyber or bioware. Not that anyone would be foolish enough to play a Samurai if they had the option of being an adept.

4. Without knowing the skill of the doctor involved, it is impossible to calculate surgery costs.

Just limit the stuff people can get through the availablity rating. Sure people may want an MP-5 but in the neighborhood you live, people don't have those, but check out this cool colt asp.

It's more relaistic than you know. When I lived in NY gun laws are really tight and it's hard to even find a gun shop. Now I live in Pennsylvania,, a much more gun friendly state. Without trying I can think of 4 gun shops within 15 miles of my house and most sporting good shops also sell ammo.

So I moived form an area where it was hard ot get htem, to a place hwere it's easier, conversely I went form an area with a much wider range of new age/alternate religion shops (talismongers) to an area where I've got to drive about 25 miles to find one.

does this mean a low level game like that has to be in the barrnes? Hell no! Maybe your characters live in a high tech, well protected area where the police do not want people to have wepaons so at best you get a hand gun. and anyone with maghical power was snapped up by the corps so they are rare too. Go to the barrnes and maybe someone's selling SMG's out the back of a jeep and shamans arem ore common because they are safe from the corps, but your nice corp characters don't want to go to those sort of places. but they do wnat to cause a little trouble in the shadows.

Does this make them weenies because htey don't tool aropund the barrens in an armored step van? No.
They are infact better placed to makev a run in a corporate are than the go gangers who enjoy nightly brawls because they understand the corp environment. After all two people are walking down the street. A guy with spiked hair and gang colors and a corper playing with his blackberry. Who'se going to be remembered by the sec team?

Money. Limit the doss the characters bring in, enforce being SINless, harass them until they live in a constant semi-paranoid zone.