Valentine's Day is the second-most popular day to pop the question, and millions of couples are expected to get engaged today. According to The Knot's 2017 Jewelry and Engagement Study, the average national cost for an engagement ring in the U.S. is $6,351, just under $1,000 more than average national health care spending per person ($5,407 in 2016). And just like average health care costs, the av...