The pre built ones are the nicest looking but you do pay for it. Depending on how big of a rack you need you can do it under $100. I got a nice entertainment center for free, it will hold 8 16 qt tubs or 4 32qt tubs. All i need is heat which is cheap.

There are alot of cabinet type deals that are cheap and look great. I think when you order a rack you pay for the looks and ease of moving since most are all plastic