Have you sourced the 2"ID tube? I see that as being the only issue. The base 4" material is standard 1/4" bar stock. The rib is simple and can be sheared from plate. Saying that I have always found it better to have my local laser/plasma shop nest parts like this into their normal day to day jobs. You may have to wait a little longer till they run that material but it always ends up being cheaper than I can get the material for.
Your local metal fab shop will have no issue with this (along as the tube is source able. I'm sure metalsupermarket or even mcmaster will have it) I would guess $80-100 a piece for material and fab.