Bonaparte,
Applaud your effort and it looks like a good design if the stock is beefed up AND you have the correct angle, maybe its just manufacturers saying this but have heard even 2 degree off can be a disaster.
You say $100 dollars for materials which sounds right, figure another $100 for a welder yes , from your profile pic it seems you can do that but most people cant. Then you prolly have a $100 dollars to galvanize (have heard because of the hazards and regulations only grandfathered shops still do that) .
Area im from is one of the steel capitals in America and to go pickup steel, cut it yourself, take it to a welder, drive 70 miles for galvanizing, then pick it up would add up in fuel as well as very time consuming.
So in the end costs are very comparable and if you value your time then its even more exspensive.
As a matter of fact just ystdy i was going to plop the 450 for the 22kg (48lb) rocna as I ve been manufacturing all kinds of other parts which is getting tiring and an anchor manufacture would be inefficient time wise.
Of course if you find pleasure in such an endeavor, go for it.