Since when ever has the smart thing to do been to buy the cheapest option?
If you're looking to build a complete dune bike, you should figure you'll spend $6-15k
Don't even waste the time taking your time. Just do suspension and a cub setup with shearers and be done with it. You'll be money ahead just going straight into it.
T5's are probably the best sounding/looking stamped pipe. But they aren't good for much besides that.