I don't want to give the impression that this is the way I routinely handle questions — I don't cover state government and my focus is local and county government, so I haven't had a reason until now to check. The political consensus seems to be that the beauty contest primary is a waste of money but not a major issue. I concur. If this were the worst waste of taxpayer money going on I wouldn't be too upset... not the biggest issue on my list of things to which I pay attention.
If you want me to do so, I will do some digging and post relevant links, or if for some reason I can't get the rationale online from primary sources, I will make some phone calls to verify facts. You've asked a question to which it would be helpful for me to know the answer with certainty and with primary source research, but until now nobody has asked me and I haven't yet needed to know for my own work.
We have so much wasted money its true, but a little here and a little there, and pretty soon you are talking about real money.
I think we have it better than some, because at least we have the Hancock amendment, which I do think helps keep the taxes/spending in check somewhat.