I am in the process of building a welded steel frame over 10' long for my catilevered mill.
The basis is a Steel I-beam 24" between webs, 5/8 thick flanges 10' wide, with lots of 4x4x.25 wall A36 steel tubing welded in a torsion box design on bot sides between the flanges.
The cost for stress relieving something this big and massive in Northern CA is going to be between $1000 to $1200 dollars.
Blanchard grinding the long axis is going to cost another $750.
When I look at the overall cost and affect on accuracy, it seemed like a good tradeoff vs other construction techniques.
If the frame isn't straight and flat, it will be useless, hence the stress relief and grinding.
Al