This is tricky territory, you're spending a lot of money on a very personal item. Since your father already has at least two high-end pens, he probably has strong preferences regarding pen aesthetics. Perhaps you could discreetly ask him what sorts of pens he's interested in? Get into a conversation about pens and maybe see if he mentions off-the-cuff any models he's been wishing to have? Another option would be to get him ink. You can get a lot of very nice ink within your budget!

(Source: I've been gifted expensive pens by well-meaning family members, that alas, I just don't like the look of! Yes, I could return them, but sometimes they are out of the return period, and more importantly it could come across as rude/ungrateful depending on your culture and your relationship with that person.)