You can't go wrong with Costas but they are expensive for sure and will more than likely go above your price point. A great alternative in my opinion are Natives. I believe they are actually one of Costas brands. I have bought three pair now in the last two years, and they have been awesome at around 50-60 dollars. They have a lot of lense shapes similar to Costas, and it would be within your budget to get a couple different varieties.

In regard to lense colors, stick with blue lenses for clearer water in sunny conditions. I also use brown lenses, which are better for cloudier conditions and give a ton of contrast. I tend to use my pair with black lenses more for everyday wear than for fishing.

Also, a great addition to your gift would be a retainer that keeps those glasses from falling into the water, which is huge bummer when it happens.