Fireworks are very useful for elytras and flying long distances. But the fireworks are fairly easy to make, I'd say a little less than 10r per firework
Next to whhat Gordan_the_gourd said: there are three different fflighht duration fireworks, I suggest mainly using the 1 and 3 ones, the 1's are great for building (flying around the things you have done to see iff you like it) and thhe 3's are great to cover great distances. flight duration 2 is almost never used. working with just 1 is also a possebility, you can also use that one for long flight, but with 3 it's nicer (the 3 for building is just a pain btw...)