I don't personally think it's necessary to go up to €150, but a low-quality entry-level soldering iron will cause a lot of problems, and you'll be blaming yourself for the lack of progress. I learned on a crappy one and always thought I sucked. On university I used one that was alright and it was night and day.

It is important that the soldering iron provides the correct amount of heat, and with entry-level irons it's always a gamble, in my experience.

On the other hand, spending the €150 from the start will save you a lot of time testing irons.