Congrats bro! I didn't ask her parents either, but after as long as we knew each other and living together for years it wasn't a surprise. They don't have a real close relationship so I didn't really feel the need. It matters more if they are close or if the father is old school. That said, kudos for nutting up and doing it the "right way."
Diamonds can be pricey. I bought my wife's ring from Blue Nile. Best pricing, higher quality stones than most places I walked into, and a ridiculous amount of options. Just remember they are like cigars... If you have to choose quality or quantity, always go quality... Lol