I've used fountain pens since I was about 7, as that was the expectation at school in Britain. (I think it still is, although searching a couple of British stationery shops I don't see pens covered in cartoon characters — unlike in Germany[2].) Like many children, I rebelled against this requirement for a couple of years in my teens. It is a bit unusual to go back to using a fountain pen, but I find it much more comfortable (less hand cramping?) than any other type of pen.

I used the two pens I had from around age 13 until I lost them when I was 25 or so.

I replaced them with two of very similar quality, costing €15 or so each, and marketed towards teenagers and college students [1]. They are perfectly fine. They uses the standard (cheap) refill cartridges, and I will not be particularly annoyed if I lose one.

By all means spend more if you enjoy the weight of a metal barrel, or a luxurious design, but I think there is little functional difference between a €15 pen and a €150 pen. Especially if you don't write daily.

Starting with a cheap one like this is probably a good idea if you've never used a fountain pen, or haven't used one for many years.

[1] https://www.online-pen.de/fueller/fuer-die-schule/ (I have "Campus" with a fairly plain pattern on the barrel.)

[2] https://www.online-pen.de/fueller/schreibanfaenger/ "Pens for beginner writers"