I don't know a ton about knives, but I would say this:

Buy a knife from a company that sells "trainers"--non-stabby/slashy versions of their defensive knives, made of the same materials, weighted the same, and so on. Because these are companies that are actually intending people to use their knives seriously.

Personally, I would suggest a Spyderco Delica 4 with the "Emerson" Wave opener option. It's $30 over your budget, but you get a lot for that. For $10 more, you can also get the larger Endura with an Emerson opener.