Obviously this is a neat thing and not a necessity and requires extra expense and time. That said I would recommend the following. Get a miniDV camcorder and a good tripod (like a $100 or better) and position it so people won't knock it over. I would position it so you and your hands and some of the dancers are in the shot. Have a TV so the audience can see it. In some places this won't be necessary since most wedding receptions in Bingo rooms have lots of TVs. I tie in to their main system in this situation and it's all over the room. You'll also look great if they have a big screen TV. You won't need to actually tape anything if you are simply showing the audience the shot. However if you get a DVD recorder ($150 and up) and have tape in the camera you can do the following:
1) Make a DVD of your performance and give it to the bride and groom and stick a label with your name and phone number on it. You have just given them a priceless momento and heirloom that cost you a dollar to make. You have also just given them a business card they will never throw away.
2) You could add this service as an option. I would charge $100. But even $25 would eventually add up to pay for your costs. Of course you'd want to do it for free and not mention it beforehand the first few times in case you screw it up or something goes wrong. You may want to hire a 2nd person to do this during the show, and charge accordingly. I prefer to do it all myself so I'm not screwed if someone doesn't show up.
3) You could offer extra copies to others at an event for say $10-$20 dollars and mail it to the customers. Have them actually fill out their own mailing address on a card stock DVD mailer to save you time. Again, they are getting a lifetime business card from you.
4) If you run tape in the camera, you have a video of your performance for your own use. This will be useful for three reasons: it will be fun to look at years later and see how you have improved; it will be educational for you to see and hear your actual performance as you strive to better it; and finally you will be building up a great demo video you can put on your web site or mail to prospective customers. Note this video wil be DVD quality audio if you run rca cables from your mixer tape-out to the camera. When I video myself singing and play it back over the same PA, someone with their back turned couldn't tell which was which. I've done this for grins. miniDV is that good.
5) If you get good at this, you might open up a sideline business doing videos for weddings, etc.
Note A: I bring a 2nd TV to plug into the DVD recorder to make sure I can see what it is doing and make sure my shot is alligned correctly throughout the taping.
Note B: Depending on how many blank DVDs you are using, you may want to add more or less to the cost.
Note C: It is a good idea NOT to write on or affix a label to a blank DVD until AFTER it is used. That can cause problems recording.
Note D: Good places to get lots of info are
Digital Video Magazine
http://www.dv.com Videography Magazine
http://videography.com B&H Photo·Video·Pro Audio
http://bhphotovideo.com The two magazines offer free subscriptions to industry professionals. B&H offers good prices, large pro staff, huge selection. These guys sell cheap camcorders up to cameras that cost 6 figures so they know what they are talking about.
I shoot with a Sony DSR-PD170 camcorder (about $4,000 with case, battery, light, etc.) I edit with Sony Screenblast Movie Studio ($99.) Note that camera is WAY more than you need to do a shot of your fingers and keyboard. You could get by with something from Wal-Mart. But I do freelance news for TV stations so I needed an entry level broadcast quality camera.
If anyone wants more specific information I'd be happy to expand on the topic.
I am looking for a family reunion video I did and will send a message when I can find it. In the meantime, here is a news feature story I did for the local ABC affilate:
http://mcdermottreport.com/images/bones_andyguestpark_edited.rm Requires RealPlayer.