Temporary Fender > Permanent Fender
A bike fender is absolutely critical for commuters - it'll keep you dry where it really matters. The fender I chose long ago was affordable and worked well enough, so I didn't see the point in buying a new, more permanent, one. Instead, I whipped up a piece of bent aluminum sheet metal to hold it in place.
The bracket is held in place with a bolt where the back brake would usually be (this is a fixie). Photos of the build process are below: