squid830: You can head to the Caravanserei, there's a small hostel of sorts there and you can rest there for 20 shins.
wlerin: It's 20 shins per party member. Resting with the Cultists is going to be cheaper 90% of the time, since they charge a flat fee.
In both Act II and Act III you can unlock places to rest for free after completing certain quests.
My bad, I thought it was 20 for the whole team.
And now that I have completed the game...
** MINOR SPOILERS AHEAD **
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I have not found ANY other "organisation" that it is actually possible to join. Then again, I did wipe one of them out (since they were pretty much evil), so maybe it's possible to join this one?
So AFAIK there are no detriments to joining CG's cult (even with Cal in the team, she doesn't appear to care really), but it appears to be the only way to get free rest/healing in Act I, and you get a decent discount on their (mostly useless) stuff.
** SPOILERS END**