In "At what cost, carnivory?" by Gregory Lewis, ACE's estimation was that the cost of making one vegan for one year was 4.38$ (2015) on average. The answer to improving vegan activism could be to target students and have a charity that copied and held Gary Yourofsky's "The Most Important Speech You Will Ever Hear".

Link: 

Gary Yourofsky made many speeches and converted, on average, 15-20% to vegans, and another 50-60% made a drastic change (of the audience), he says in the video below (1:23-1:44). Paying someone 10-20$ to hold a speech would be reasonable from a cost-benefit perspective (or maybe they want to volunteer). Perhaps some of the four he convinced to be vegan will be it their whole life. Then it could have the potential to be the most effective way to make people vegan. It could be interesting to see an implementation of this idea in an organization and a test of how it would work out. 

Link: