You know you like it and that Beyoncé told you to put a ring on it, but you don't have Jay-Z's millions. How do you do right by your lady when the money isn't rolling in? The decades old rule of thumb is to spend two to three months' salary on an engagement ring, but if you're just making ends meet, dropping a quarter of your yearly income on one piece of jewelry may sound insane, despite its significance.

Assuming you're not a lunatic who goes around proposing to random women you meet on the street, your fiancée-to-be knows you and your financial situation. When it comes down to it, most women would rather have the less expensive ring that lets you keep your own place than the expensive ring that makes you pack up and move back into your parents' basement.

Spending trends

Lee Cronk and Bria Dunham of the Rutgers University Department of Anthropology and Center for Human Evolutionary Studies found that, despite the two to three month “rule” for engagement ring spending, married men spent less than 9 percent of their annual income on the engagement ring of their wife — around one month's salary. Clearly, the wives still said, “yes.”

Before you start shopping, figure out your two-to-three month salary and see what kind of price range that puts you in. The average engagement ring cost $3,500 in 2012, so that's a good number to keep in mind, but adjusting down to a more affordable budget may be a less-stressful start to your married life.

Many couples are now choosing to make engagement rings a joint purchase. That doesn't mean the proposal can't be a surprise, though. With the money you save, you can focus on making the proposal something she'll never forget.

Diamonds, the permanent trend

There's no getting around it, diamonds are expensive, and the bigger the diamond, the more it's going to cost. You probably know, though, that size isn't the only important aspect of a diamond. The color and clarity are also essential elements of a diamond that sparkles on your girl's hand.

Diamonds are traditional, and you may have a non-traditional girl. Hold off on the "she's not that kind of girl" mentality when it comes to picking an engagement ring, though. Diamonds are so ingrained in our society's standards as proof of engagement that your non-traditional fiancée may spend the first weeks of your engagement confirming your engagement if you opt for something other than a diamond. As a general rule, your girlfriend will not be disappointed in a diamond ring unless she’s specifically told you that she would be.

That being said, you know the woman you want to marry, and that can help you when you go ring shopping. If she’s non-traditional, look for things like fancy cuts to give her ring more personality. If you have a few ideas about what you think she'll want, but you're not completely sure, consider asking one of your girl's friends or family members — one who won't give away your secret — for help.

Whatever you do, don't let shopping for the engagement ring stress you out. Figure out a budget that won't put the hurt on your finances and shop around for something in that price range. If you think your girl deserves more than you can afford, remember that you've got plenty of time. That's kind of the point of getting married. A few years down the road on a special anniversary, if you're so inclined, you can always make it up to her.