The minimum requirement is to let the woman know you care.
The least expensive way is to look at her
-- preferably somewhere on her face -- and say,
"I love you, [her name here]."

If you forget her name, don't bother with the rest of the steps. You're dead.

A Valentine card is an acceptable nonverbal token of appreciation. Best of all, it's cheap.
Good Valentines are pink with lots of lace and have cute words such as,
"I'll love my sugar bunny forever and ever and ever and ... "

Bad Valentine cards say, "Good for one free quart of motor oil."