I have some good news and some bad news.
The good news is that yes, Ubuntu is free, unlike Windows, for commercial use (Windows now requires an Enterprise License for commercial use, and while you could still operate your company with a non-commercial license, why risk the ire of the BSA?). Not only that, but most of the applications that Ubuntu ships with are free.
If you need a word processor, spreadsheet, database, or presentation creator, they're totally, absolutely, legally, free. If you need audio mastering programs, they're free. If you need graphic design programs, they're free. If you need 3D modelling tools, they're free.
Here comes the bad news: you're probably not used to Linux. Yet. Canonical, the makers of Ubuntu, strove to make Linux as user-friendly as possible. However, if you're anything like me, you're so used to Windows/Mac OS X that when you need to change/alter something and find that things aren't exactly analogous to where your old operating system has them, you're going to get a little annoyed, even frustrated.
You are not alone.
Luckily, you're not the only one. I'm saying you're lucky in this regard because, more likely than not, any problem you've had, as a beginner Linux user, has been experienced by hordes of Linux users, and even more luckily, almost all of their solutions are well-documented on the internet. All it takes is a little Googling finesse, and you'll find your solution in no time. I'll have a post on how to do this in the near future.
Hold your horses, you might be thinking. People generally dislike being told they're beginners, especially when they're running a business. Afterall, a beginner using a tool will never be able to maximize its potential as well as an advanced, or even intermediate user. Why don't I stick with Windows or Mac OS X, which I know well enough to get things accomplished?
The reason is this: Beginners transitioning to Linux and Ubuntu can still be just as productive. The applications are the designed to perform similar functions as the applications developed for Windows/Mac OS X. Like I mentioned before, the applications are typically free.
Furthermore, Ubuntu is designed to stay out of your way, so that you can get what you need accomplished. Practically every use of your previous operating systems can be replicated on Ubuntu. Hardware and networking support is a snap. Installation of almost every driver or interface is automated (however, you should look into upsupported/troublesome hardware lists just to make sure you're going to enjoy full support before making the switch).
What's more, if your employees typically do most of their work on the internet, studies have shown their transition to Linux will be even easier. If most of their work takes place inside a web page, then their auxillary tools like text editors and programming IDEs easily have analogous editions or replacements.
If security is an issue, it is also much tighter in Linux than in Windows. Windows has countless viruses, exploits and malware stalking its perimeter, while Linux generally enjoys a penetration-free existence. That's not to say that exploits and malware don't exist in the Linux environment. Their numbers are simply much smaller and are less likely to compromise your system. Linux provides protection for virus and exploit for free download. Commercial protection also exists.