When there is no free alternative to what you are doing, they'll still buy (in my case that was hosting).
Otherwise, your best bet for getting developers to buy things is to try and sell them stuff that would be boring for them to build. Most developers I know would find it very interesting to build something with machine learning or to re-architect a system several times over for scale. Not many of them would like to spend time building something better than textmate.
The problem with being a developer building for developers is that if you are interested in working on a problem your customer probably is too. People would prefer to pay you to take out the garbage.
Otherwise, your best bet for getting developers to buy things is to try and sell them stuff that would be boring for them to build. Most developers I know would find it very interesting to build something with machine learning or to re-architect a system several times over for scale. Not many of them would like to spend time building something better than textmate.
The problem with being a developer building for developers is that if you are interested in working on a problem your customer probably is too. People would prefer to pay you to take out the garbage.