When you consider that there is about a grand worth of materials in a 4 inch mild steel system, all said and done, $4k seems a bit steep for my liking.
For that money you could buy a sweet welder and other tools, do a welding course and make it yourself!!
Of course this isn't for everyone and that's why we pay a little more to get a hassle free, high quality, guaranteed proven, walk in and walk out experience.
I concur with Stever, there would want to be a month's worth of wristies for that price.
It's honestly less than a day's work for a bloke who knows the tools.