How do you make a 'permanent teleportation circle'

So when you use the (very useful and relatively cheap) level 8 ritual Linked Portal it can take you to a permanent teleportation circle. The permanent teleportation circle has a, well, address that you can memorise so you go to the right place. The ritual description says most temples etc have one of these. How about if my PCs want to make one (and they will!) in their own house, or just outside the dungeon or whatever?

How do you make a permanent teleportation circle, what does it cost?

Cheers

Yay Stargates!

*cough*

I'm not actually sure, unfortunately.

Sounds like perfect ritual fodder to me. I'm guessing it will be covered in Arcane Power or something like that.