A great, inexpensive date for a day or evening is to create a memory album. All you need is a couple of cameras and you're set.
If you both have digital cameras, then those will work wonderfully for the date. If you don't, then going to a local shop and picking up two inexpensive disposable cameras will work just as well. It isn't the quality of the photos that really matter, but the fun in taking them and recording the evening.
Once you have the cameras in hand, create a theme for the day or just take any crazy photo that comes to mind. You can structure it as much or as little as you like with the main focus on recording the day or evening with the photos.
Once you have finished, you can take the cameras to a 1 hour photo shop to have them processed. If you used digital cameras, you can head home and load the photos into a computer.
At this point you can create a memory album of the day/evening with the photos you took. If you don't have the time, you can delay and make the creation of the photo album itself into another date. Either way, once the album is complete, you will have a record of the date that'll last forever.