My daughter takes her open water cert next weekend
What’s a serviceable dive knife under $50?

I gave her my favorite benchmade when she became a paramedic; I’d like to get her a serviceable knife or tool for diving.

NVM
I bought one.

Line cutters are better than knives. Some people even carry paramedic shears.

Dive knives are expendable. They're just a tool to get you out of a bind.
They're not something that'll become a family heirloom sometime down the road  

It's surprising how many divers lose so many dive knives. Dummy cords for the win, you know?

So, yeah, if she's going to lose it, buy a cheap stainless knife. It will eventually rust unless she is super-OCD about cleaning, drying and oiling.

At that end of the scale for $50 you can literally buy her a box of knives and she can use one until the rust becomes unbearable and then throw it away. I like knives with skeleton handles because things get real nasty under those molded plastic handles. For example:

https://www.amazon.com/Tactical-Stainless-Spearfishing-Snorkeling-Outdoor/dp/B0748K9N62

Just shit-can the paracord wrap.

If you want something that will be more of an heirloom you can find cheap Titanium dive knives between $50 and $100. You do have to be a bit cautious about Titanium at that price point. Amazon and eBay are the places to go. Buy on Amazon so you can return it in case you get a fake. Buy her a retractor type dummy cord for it, too . You can always cut the retractor cord with the knife if you need to in an emergency.

Some places prohibit diving with knives. "Dive shears" aka EMT shears are cheap and disposable. I've never seen a real Titanium one. They will try to rip you off by advertising a "Titanium coating"--don't bother with that shit. At <$10 you can get her a couple of those and a couple of the cheap knives. Then she can mix and match as she develops her own diving style and preferences.

And of course there are the ubiquitous line cutters. Those are somewhat less useful than dive shears but possibly easier to use in an emergency. Mares makes a real sexy one with Ti and ceramic. I've seen it advertised for $50.

Since she’s already a paramedic, tell her to just use a pair of paramedic shears. So many people lose dive knives like you wouldn’t believe.

A dive knife should be small, with a blunt tip (like a sheeps head profile) because it is used for line-cutting, not stabbing. A pointy tip is a liability.

Many of the best divers in the world just use steak knife broken off at 2 or 3 inches and rounded off.

Anything with a sub-4inch blade with a blunt tip should be good.

I carry a short blunt knife and EMT shears and so does everyone I dive with.

I have a titanium one that was $45 and real titanium. So light i forget it is there

I'd wager that is titanium coated.

I carry EMT shears on my shoulder strap, and a Trilobite line cutter on each side of my waist belt (I dive a BPW setup).  I dig knives and always have.  I've owned "dive" knives and carried them on me when I first started out in college.  I've since matured and realized that the EMT Shear and Line cutters make way more sense for most divers.

However....if you really want to get her a dive knife.  The Spyderco Salt series is awesome.  I believe they offer folding and fixed blade options.  I keep the folding version in my dive bag and travel with it since it is bright yellow and "hides" real well with the rest of my dive gear.  I clip it on my harness sometimes and dive with it, but mainly use it topside and out of the water.

Here are two great vendors that I highly recommend for shears and line cutters:

Piranha Dive Mfg.

Dive Gear Express