I mix yeasts regularly. I reuse yeast and sometimes mix (similar) types to create "unique" fermentations. Some brewers really like to hit the BJCP style right on the head. I only try to brew good beer. I don't always do that but I like the challenge. The only problem is when you create a super beer replicating it is nearly impossible. To me it's not the price of yeast it's creating beer that I make and I drink.