did not hear about such sensors used in the DYI projects. They are way too expensive.
Strips or liquid tests will do the job, as @PlantedRich
already mentioned. Usually, you use Amonia and Nitrite only after you setup the tank, and once that is balanced, things are ok, and your test is sitting unused.
Nitrate is the only one that a planted tank has to keep an eye on, especially if there is a fertilization going on. But again, once you know your regime of fertilization, you pretty much know what are the levels, and check them from time to time, and yes, you need just the ballpark of the measurements.
So, I would not bother with spending money on that
unless is as cheap as a Ph probe (and I do not use even that one in my Arduino iAqua built)