We like to relax pull out the paper plates and plastic silverware and order take out. Sometimes we go for a walk together. You could always go on a picnic even if in your back yard.

How cheap are you needing? Maybe try something like bowling or ice skating? Walking around the flea market or farmer's market is usually fun too

We like to base things on what's in the area and the time of night it is. Typically my partner works long hours. Although that works for me (I'm a major night owl) this can limit things a little. Here's a few of our less pricey favorites.

Hamburgers, then hitting the arcade.
Nothing's more fun than junk food and playing around like a teenager. Well, nothing you can do in public, anyway! Typically runs about $15 as we like to use coupons for both places.

Subs at the local bar.
There's a little mom and pop place down the street we like to visit. We grab subs, beer (root beer for me- I'm usually the one driving), and watch the game while chatting with the drunks. Typically runs about $20 including tips.

Window shopping!
You don't always have to buy things, sometimes just hunting them down and looking at them is just as fun. I use this as an excuse to figure out what to give my partner later by taking note of positive reactions. I always look like a curmudgeon when I say no to buying right then and there, but when the wanted items mysteriously show up later the smiles are impossible to miss. This is free.

We play strip board games. Lately it's been Seinfeld Trivia. It's loads of fun and introduces a bit of playfulness!