The media news network CNN sent reporter Nic Robertson to the border of Saudi Arabia and Yemen, where he was given a tour and saw several of the Yemenis caught smuggling over the border. One of the items being smuggled was qat. A young boy was given $50 to smuggle it into Saudi territory. The authorities tell him that in the past three months they captured close to half a million tons of qat worth 100 million dollars on the street. Here is one way the Huthis are getting cash. The report indicates that the Saudis are spending a lot of money to build fences and guard towers, although much of the border is so rugged it is impossible to stop everyone. Robertson is a bit overactive in his role at one point telling the Saudi interior spokesman with him that the Iranians are behind the Huthis and then saying this is what the Saudis say. I suspect it is what the Saudis say, but it was presented as a statement in the excerpt provided.
You can watch the video here in English, here in Arabic and read about it in Arabic here.