Sounds like that was an estimate to replace a niche on an inground pool. That likely involves breaking up some of the concrete to do.

I would find a light that fits in your current niche. You do that by finding the brand of your current light or niche and buying the same brand.

That "container holding the bulb" sounds like a typical light. Here's a photo of my old one (with the glass front removed) before I replaced it with an LED.