Hello Zosia.
Assuming that you don't want to bother with the manifold problems which arise from using a dip nib in a fountain pen, here are a few options:
If you shop around, $50 should get you an unglamorous but serviceable vintage pen - chances are it will take a bit of searching to find it though. The advantage of this is that you'll get a feed which is matched to the nib. Fine points are fairly common; extra fine are not. Waterman and Mabie Todd nibs are both names worth looking out for, but there are less well known brands which work just as well. Since you are within the EU, you might want to have a look at
Goodwriters and
Write Time, both of whom I've had dealings with and can recommend. Especially Goodwriters: if you send Deb an email she'll probably be able to sort out something suitable within your budget.
Secondly, instead of an Ahab, get a Noodler's Nib Creaper and search for an old Waterman #2 nib. The smaller nibs can be had much more cheaply than the #6 which fits the Ahab. The thinking here is that you get an adequate pen body with an excellent nib which will definitely fit, although you will need to do a little bit of work on the feed. That isn't as bad as it sounds ... well, all right, you'll get covered in ink and ebonite dust, so it's pretty bad.
Thirdly: buy a Noodler pen, or have a look at
Fountain Pen Revolution. Either way you'll get decent value for money. Some people are really down on these cheap pens, but I've had a few and they all worked okay without modification, and really rather well after a bit of work on the feed. The nibs are by no means fully flexible or even close, but they do have enough spring to get some worthwhile contrast into your writing. Of course, if you go for the Nib Creaper you can always keep your eye out for that Waterman #2 and still have a functioning pen in the meantime.
In the end, vintage flexible fountain pen nibs beat new ones hands down every single time, regardless of price. If you can possibly budget for one, that's the way to go.
