At 75€ per hour, visiting one of Paris' "Love Hotels" is not an inexpensive Valentine's Day idea. But you'll definitely get your money's worth of intrigue.
The love hotel trend is very popular in Japan, where many young people living with their parents have a hard time finding alone time. There, you can rent themed rooms inspired by anything from Hello Kitty S&M, to the Titanic, to a gynecologist's office (really). But the Parisian offerings promise to be romantic, charming, and luxurious. The site dayusehotels.com lists all hotels in the City of Lights offering rooms by the hour.
The My Little Paris daily newsletter proposes that you send your lover a text on Valentine's Day saying "Rendezvous at 1 p.m. at this address." When he meets you there, he'll be surprised that you've secured a hotel room. I have to admit, it sounds kind of hot. But could you bring yourself to secure an hourly hotel room, even in Paris?