I agree 100% percent with the other posters, but I wouldn’t dismiss the Wilton classes entirely. And if you have a Michaels Craft store near you, you might be able to get the class at half off. My Michaels seems to always be running a half off or BOGO deal on the Wilton classes. If you’ve never decorated, it’s nice to start out with some instructor based training. You might also want to see if there’s a decorator’s club in your area. They usually meet once a month and they will discuss new techniques and even have demos.
Cake decorating in itself is not a cheap hobby. The $25 (or 12.50 if you catch a deal) for the classes are a steal compared to the tips, pans, sugar, butter, eggs, etc. you will be buying.