This is well outside anything I can claim to know much about, so I can’t vouch for it other than that it sounds right to me. From an Al Arabiya article entitled All you need to know about the Iran protests in 20 points:
1 On Tuesday, December 19, the Iranian government announced a new austerity plan.
2 The plan imposed a 50% increase in the price of fuel.
3 The government decided to cancel the monetary support of more than 34 million people.
6 In this same austerity plan, the government decided to increase the budget for military armament.
7 Most of the military armament budget goes to the Iranian Revolutionary Guard Corps (IRGC).
8 The IRGC operates on foreign lands, supporting the Houthi militia in Yemen, Hezbollah in Lebanon, the Popular Mobilization Unit in Iraq and supporting the Assad regime in Syria.
9 The number of poverty-stricken individuals under the lifting of subsidies rose from 20 million to 54 million.
10 On Wednesday, December 27, citizens went out on a limited demonstration to demand that the government backtrack on the austerity plans.
And… its grown from there.
My limited understanding of Iran is that the religious authorities have kept a grip on power -despite being disliked by the urban intelligentsia – by maintaining support among the poor. That makes choosing guns over butter particularly stupid.
Update 12/31/2017, 9:43 AM PST: Here is another piece on the protests in Iran from the same website.