Is it possible to enter a cartel with HM2 or do we need PT4? And if you don't want to purchase it, what will happen if i just sit everybody at the $30s anyway, will the stronger players attempt to bring me down stakes assuming I am beating the weaker regs(likely not going to happen at first)?
I'm not sure of the answer to your questions.
If you are required to buy PT4, even if you can still get into the $30s group by beating up weak regs, I'd imagine buying the software for $100 to get chip EV or whatever the requirements are is best.
Now, they may not require you to buy PT4, I don't know if the HM2 stat for chip EV/EV ROI is the same as PT4 now (I believe they are not the same though). So I would just ask one of the leaders in the division about the rules and go from there.