What Laptop Can Run Minecraft Shaders on 45FPS?

Laptops aren't as good as desktop, and I can't recommend a specific one since you're in the US and I'm in the UK, but I would look for a laptop with 8GB of RAM or higher. Try to get an i5 (if you're going for the Intel side) or try to get an FX series laptop (for AMD). You will need a graphics card that has at least 1GB or 1024MB of VRAM, but try to get a 2GB card. Any higher and it would definitely spiral out of your budget price, and you'll be lucky to find a laptop with a 2GB card in your price range (at least from what I've read up about US prices).

You need a 64-bit operating system to handle 8GB of RAM, just remember that. It doesn't matter what OS you get, but a particular favourite among PC gamers is Windows 7 64-bit. I use Windows 8.1 64-bit, and that can handle 128GB of RAM (if you could afford it!) whereas Win 7 64-bit can only support 16GB, which is more than enough for Minecraft anyway!

Hope I helped, and have fun playing Minecraft!