Infrared filters for drone cameras

I'm interested to know how people are going about acquiring infrared imagery from drones (e.g. to calculate NDVI). There are dedicated cameras out there, and also camera conversions are available. I've also heard of cheaper DIY alternatives. We have access to a multispectral camera but we also support a fleet of DJI Phantoms, Mavic Pros and Inspires which are flown by reserves staff and ecologists rather than technical experts. What are people's experiences / recommendations? We're particularly looking for low cost solutions but needless to say it has to be fairly robust also.