The Getting Started In Woodworking (GSIW) Workbench is cheap and easy to build. If you have a circular saw, drill, router and a need for a decent bench I would highly recommend giving this one a shot.
Detailed instructions (including video) can be found over at finewoodworking.com, so I won't go through it step by step. I'm just going to point out the more clever stuff.
Step 1: Routing channels for the allthread
This GSIW bench is held together with allthread laying in channels. Here's the set up they recommend for holding the 2x4s. I also added a strip of trim underneath to give a little more height.