I've got three players wanting to craft their own foci, to avoid the sky-high costs of buying them. Two F3 sustaining foci and a F3 power focus. This session, they created the formulae (the two Hermetics teamworked the power focus and one of the sustaining foci, while the shaman designed his own sustaining focus), and we talked a bit about the actual creation process.

One subject that came up was a workshop where they could do the actual work. I'm virtually certain I've seen rules for renting a shop or facility, but I cannot for the life of me recall where. Help a chummer out?

I can't remember any rules about renting workspace off the top of my head.

But there are a few other options: Either they buy tools at the appropriate level (the rules for this should be in the focus creation chapter of Street Magic), or you can up their lifestyle costs by 1 point (see Runner's Companion, lifestyle option 'Workspace'), signifying that they have a work space available.

What's the cost of a lifestyle big enough to house whatever workshop they need, using the rules in Runner's Companion? Stat it up as a safehouse, and charge them a bit more for whatever time they need (round up to days or whatever).

Actually, I've got my book here. A shop is middle lifestyle necessities, and a facility is high lifestyle necessities. Page 160, and it includes an example.