There are a few options:
1. You can do it yourself — record your screen while you do the demo, toss the video into iMovie and add a voice over / captions on the screen for guidance. Benefit is it's fast and free. Con is it will likely be low quality..
2. Go cheap — you can use a site like fiverr.com for a cheap option. You can spend a bit more and outsource on ODesk. Benefit is low cost, con is quality won't be too great.
3. Go big — hire an video agency, develop a story / script, proper film production. Benefit is the quality, con is the cost (though you can likely find decent options for around $1k, but the good companies will charge >$5k)
In the end of the day, it all comes down to what your budget is, what your goals are with the video, and ultimately, who your customer is (if you're a consumer facing product, high production value goes a long way in my opinion).
Happy to chat a bit more if you need some more in depth insight. Good luck dude!