There's a lot of bends and joints in a rack. How much is your leisure time worth? If you search, you'll find that some folks have made racks from hydraulic/brake tubing of ~ 8-10mm outer diameter. Most cheap bike racks are made from solid aluminum rod, but steel tubing would be stronger and far more fatigue-resistant, and probably lighter.

Nashbar always has deals going, and usually has a dozen craptabulous (meaning not so great) racks for sale. They had a 25% off sale yesterday.

Be aware that cheap racks are cheap for a reason, and that reason is seldom obvious from a computer monitor. Many racks fit only certain bags, frames and forks well, and vice versa. Bear this in mind when selecting racks and bags for your bike.

Peterpan made a custom rack - you might want to PM him with your questions on this topic.