Buying an engagement ring

So, I’m looking to buy an engagement ring for my gf…But it dawned upon me that I have no idea how to go about looking for a decent ring… I know that my gf would like it to be white gold, diamond, round/square/oval in shape, and size 7…

Is it possible to find something like this for around $1000 or so? Any tips on picking such a ring, where to shop, major chain? local stores? any advice would be appriciated…