Why would the new roles even cost anything? I didn't get that impression at all.
As for the purchase of things within the activities (if required), I'll wager that these will be in cash or both. I don't see R* locking progress like that exclusively behind a pay wall.
As far as earning cash, I've never really had too much of an issue. IMO, it's never been too difficult to earn money through hunting or just playing missions, etc. to buy what I needed. .....then again, I don't waste it either on frivolous stuff.
I usually keep around $1,000 on me and try to maintain that balance so I have enough cash for things I need as they come. .....but you do have to grind for it. On the other hand, I've been surprised how much I can earn when I just forget about it and play a bunch of missions / activities over a few sessions.