Sites to buy Engagement Rings?

Hi, I’m wanting to propose to my girlfriend of two years sometime in the next year, and I was wondering if anybody knew a place online to get a ring that won’t break the bank. We’re low income, but I want to get her something pretty. She’s shown me some sites before but I forget what they were, and I don’t wanna ask because if I do she might catch on and I want it to be a surprise. We’re kinda gothy, and her favourite colours are black and green. I was thinking a black ring with an emerald (or something). She’s not a fan of gold so i was thinking dark silver (if thats a thing?).