I agree that this case will come down to the money, but I do think it was about theft of cash (and probably also product) on hand. The thing is, if this was business, it was a terrible business decision. Anyone who has been in business with the Rhodens, or even has illegal business in Pike County at all, is going to be negatively affected by all this LE attention on their actions. With all these anonymous tips flowing in, LE is likely to know every drug dealer in the county by the time it's all said and done. It's hard to imagine how someone could be rational enough to plan out an execution of eight people for turf protection and at the same time think that somehow killing eight people would blow over and wouldn't affect their turf. If it was clear who sent the message, then the killer would know that word would eventually get back to LE that they stood to benefit.
It feels to me like the extent of the killing - going out of their way to kill everyone in the family - was done in order to silence anyone who might have known that a deal was going on. It seems likely that the initial deal was being done between the killers and CR Sr./GR - the killers sprung their trap on those two and tried to get info from them, probably where money or drugs were located. I suspect CR Sr. & GR fought back and refused to give up the location. That is when the killing started. First, Frankie & HG. They still wouldn't talk - then DR, CR Jr. and HR - maybe they had already killed CR Sr./GR by that point, maybe they got the info from DR by threatening her kids. Then they realized they'd gone too far, so they killed everyone in DR's house too, in order to cover their tracks. Then they drive to KR's house - that is where the stash was - they don't need to question him b/c they already know what they are looking for. He gets shot while still sleeping, they grab the stuff and get the cameras that were trained on the hiding spot, which DR or whoever spilled the secret also told them. MOO
The fact that the reward was rescinded and that LE has been so quiet indicates to me this was not a cartel action - if LE was worried their killers were already out of state and on their way out of the country, they would have appealed more to the public for help. Given that they are keeping their cards so close to their vest, I think they have a lead on who the perpetrator is and are just waiting for DNA to tighten the noose. The killers eliminated eight people, but in a small town like this, more than those eight were likely to have known who might be doing business with Sr. & GR.