Just be careful with the budget opera recordings. Many of them have terrible sound quality. A lot of the super cheap recordings come from live recordings taken from the house by just a handful of microphones and they often have a quality similar to bootlegs that were taken by somebody near the back sneaking out their portable cassette recorder.
Once you have an idea of which recording you want to reference I would suggest first checking your local library, as many opera recordings run on the expensive side. On the bonus side, by checking with the conductor or company which recording they recommend the odds of them having a copy that you can borrow are pretty good as well.