The decision to buy a knife depends on what you are using it for. A good knife treated properly will be the last one you ever buy.
I have cheap knives and I have a couple very expensive Wustof's that are well worth the money for the time and effort they save me. It depends on how often I use a knife, and what it's for.
I normally do pithing, so a long cheap fillet knife that I got for .99 cents works just fine for that. I just have to watch the point and make sure I don't try to stick it into a rock or something.
For the kitchen I have my Wusthof's. I have a 6" chef's knife, a paring knife, and a set of shears. That's what I use for butchering chickens into parts when I need to as well as chopping vegetables. They hold an edge like a lifeline, and I can slice through tough meat and reduce a chicken to it's parts in under 2 minutes. Cuts through joints and bones like butter.
That's my two cents on knives. Make sure you keep them clean and dry, cut on soft surfaces, and inspect and sharpen before you start and you'll do fine.
And remember: A sharp knife is a much safer knife!