I could get well below $50 for lasered steel 2 and 3mm plate.
I build 3D printers and other stuff in the Philippines, so my costs for some items are really low.
One of the things that attracted me to the project is your use of steel pipe and bearings vs linear guides.
I have been searching for a CNC machine design for the last 2 years, that does not require a lot or no parts from China. Ordering from China, I pay more than what I would if I was to buy in the US. Linear bearings, guide rod, and ball screws are crazy expensive here. A order of $300 in ball screws and smooth rod will cost additional $400-500 dollars in shipping and customs.
On the other hand raw materials like steel plate, laser, water jet, delrin and machining if done locally I can match or beat China prices.