throw overclocking out the window if you don't already know what you're doing. if you mess up, you can seriously damage components. if you ignore my warning, OC at your own risk.
buying a gaming desktop is your best option in terms of price:performance, but if you NEED a laptop then there are gaming laptops that will run games on Ultra (however they are at minimum $1000)
I don't recommend an external GPU. you'll have to buy one of those things in a previous post that holds the GPU, and the GPU itself. this is not worth the time and money put into it, and for the same money you could buy a better GPU for a desktop.
if you do decide you want an external GPU, keep in mind no matter what GPU you choose, you will *never* get the same performance from it on any laptop as you would on a desktop. they're also quite large, so if you're looking for portability, look elsewhere.
in addition, to use an external GPU you also need a monitor - adding even more to the price.