These would be my first choices:
-Mora or other thin bladed Scandi with a stainless steel blade. Simple, utilitarian, very affordable.
-Spyderco Salt series. It's a pity that Spyderco only makes two fixed blades in H1 and they are both serrated sheepfoot designs (three if you count the Warrior, not a fishing knife for sure). If you don't mind serrations, then the H1 Enuff would work. Otherwise a Pacific Salt, although I'm not a fan of having a folder when I can have a fixed blade.
-G. Sakai makes a couple of fixed blades in H1 that would be very good fishing knives. The yellow Sabi Knife 6 is within your budget and quite nice, I'd take it over a Mora (just because it's cooler) and over the Spyderco Salt knives as well (it's cheaper than the fixed blades, has a plain edge).