Inspired by the recent GM Screen
video, I looked on the rules for Artificing.
In short, if you want a really strong focus you need to be a very, very good artificer.
But if you just want to dabble, the situation looks a bit different.
Let's assume you came late to the enchanting game and/or are a newbie in general.
Magic 6, Arcana 1, Artificing 1 (With Jack of all Trades this takes 2 Karma)
Creating a Focus Formula for a F1 Focus takes only 1 success on your Arcana+Magic test and one day of work.
For the Telesma you want something as basic as a stone you drilled a hole into, or some crude brass knuckles - just make sure it's as natural as possible and only has an object resistance of 3 dice (this is usually no problem except for weapon foci, but such is life. Time to learn the club skill and use a home made staff)
Now, paying Force in Drams is pretty trivial at these low values. A power focus would cost 120 Nuyen in reagents.
Staying one day in your lodge isn't to bad, but now you have to try to beat the Object resistance + Force with your 7 dice. And a Limit of 1. Which is a problem.
And here comes the cheese.
Very wisely, the rules prevent you from spending edge to raise the limit - but there is nothing preventing you from first renting a place with an artificer workshop (special work area +2 to relevant limit +1000 Nuyen to rent), calling a spirit for that one day, so he can make an untrained teamwork check (+1 dice +1 to limit) and/or have your friendly team lead around for some motivation (Leadership test +1 dice +1 to limit) - actually if you can get enough teamwork friends together you can raise the limit arbitrarily high (although it might get a bit too cozy in your lodge - three other magic types is usually enough).
To prevent glitches from eating your essence, you should definitely employ a spirit with the guard ability
That done, you are looking at a mighty dice pool of 8 vs. 4, Limit 6.
Feel free to spend some edge to get more hits - even if the limit doesn't increase.
Why all this?
Because of this little sentence in the rules: Core p. 307
"At the end of the crafting time, it is time for the dangerous part of the process: invoking the power of the focus. Make an Artificing + Magic [formula Force] v. formula Force + telesmaís Object Resistance. This counts as the culmination of all your work over the days, so you canít use Edge for this test. Your net hits from this test, if you succeed, become the focusís actual Force.
With a bit of luck you now have an R6 Power Focus for a total Karma investment of 8, 2 days worth of time, 1120 Nuyen, and a few favors from your friends (maybe they want to hang around a bit more to get their own foci?)
And yeah, I realize this is blatant abuse of the rules and no sane GM would allow this...
But I find this pretty neat nonetheless