What kind of yeast you want to make? If you are talking about yeast for bread, you can start it with very low cost. I make it by dry up my sourdough starter on a silicone sheet, collect them and give it to my friends. The dry yeast can be kept for years without problem. I think it is possible to scale it up and make it a business.  The material cost is minimal.  You only need bread flour and water.  A bag of 1 kg bread flour is only cost about US$2 or less and can be used to make close to 100 packs of 10 g yeast.

Yes, I am talking about bread yeast. 

Thanks for your kind information.