Salary
Average Salary: $1,500
Expected Lifetime Earnings: $62,622
You don't have one.
Okay, that's technically not true. If you manage to publish a greeting card or two, you'll get a little bit. While greeting card writers can make their money in the form of a flat fee, licensing fee, advance royalty, or some combination of the above, they typically receive a teensy-weensy flat fee (source)— around $25 to $150 per accepted submission, with humor and "punchline" writing raking in the higher amounts (source). Lower compensation goes to the more glutted verse market.
If you're really a greeting card fan, keep in mind that the average commercial greeting card costs between $2 and $4 (source). Using some of your earnings, you'll be able to afford one of your own cards—so long as you save that $2.50 tomorrow when you skip your next subway ride and walk the three-hour commute to your friend's house instead...