is about $350-$450 max. The APS-C sensors likely now cost $20 to make.
You're quite misinformed if you think sensors are that cheap. Think $1k for full frame and $100-200 for APS-C. Again, it's REALLY HARD to make huge chips with no imperfections. A single dust speck or mistimed/mismeasured fabrication step is much more expensive for a full frame process where only a few chips fit on a wafer than on APS-C, which fit many more. Every possible cost is squared and then some when building big chips.
I am not mis-informed, I have a ton of experience in electronics manufacturing and the costs to do so.
Canon has improved processes and switched to 12 in wafers which, along with improved high resistivity wafer manufacturing process technology has vastly improved the yield. Its why the cost of FF bodies has dropped.
However, you only need to work backward from the selling price to become aware that the direct cost to manufacture a Camera is far less than the selling cost.
The direct cost is the actual cost of the parts, and the labor to assemble them.
less Dealer markup
Less Canon North America Profit
Less Canon Japan Profit
Less Canon Warehousing / Inventory Costs including wages, taxes, facility cost, etc
Less a allowance for Service (Canon Repair facilty & warranty Costs)
Less Losses for broken, damaged, stolen items
Less insurance, both liability and catastrophic damage insurance
less shipping costs
Less Advertising Costs
Less Amortized Tooling Costs
Less amortized Development costs
I'm only roughly touching some of the costs of doing business beyone what it actually takes to assemble a product, which is why the final selling price tends to be a multiple of the actual direct manufacturing cost.