Pedalling Machine Worth The Money?

I work from home, so I live a somewhat sedentary life. I've been running a lot at night, as I need to go meet my wife after she's done work, but that's only ten, maybe fifteen minutes of exercise. I'd like more each day, so I've considered picking up a pedalling machine - basically the pedals from a bike on their own, with some resistance to make the pedalling harder - to use while I'm working. I've read they're usually used more for therapy, though, so I'm not sure if it would be a waste of money for someone who's looking for a more intensive exercise. Anybody got any experience with these? It's much cheaper than a full bike, but I don't want to waste my cash on something I'll toss out in a month or two.