Coming up with affordable date ideas (especially close to expensive holidays like Valentine's Day) can be difficult, but open mic nights and comedy clubs are great ideas for a memorable evening for two that that won't blow your budget. Image from jus10h.
Tickets themselves usually aren't very expensive, but you can also look for open mic or comedy nights at local bars, since they tend to require you only buy a drink or two instead of a ticket and drinks. Even if you go to a local comedy club, tickets often aren't too much (I've been to comedy clubs that cost only $5). You can also plan these nights as a last-minute, "I forgot tomorrow is Valentine's Day" date since many comedy clubs have tickets available at the door.
As for open mics, don't limit yourself to just music. Ask at your favourite bookstores and coffee shops if they have free literary readings from local authors. If you're not sure where to find events like these, check out local sites which compile nearby events.