Regarding a step drill bit, are you referring to a unibit? Those work well, but you're right, they are expensive. I used a standard high quality hole saw. I stacked wood up underneath the chasis to raise it up 1/4" to 1/2" or so, then clamped that to the drill press table. That helped give it a fairly clean cut, then I used a simply deburring tool to smooth off the edge. It worked great, and these tools should be easy to come by, either purchased or borowed. Always make sure to use a center punch before drilling. Even a tightly clamped drill press will wander a bit if it's allowed to!
Braden
