My theory is that the manufacturers are having to sell cars cheaper to compete with the increasing tide of european imports and the 3 year warranty on most cars comes at a price.
To conteract this they can quite easily make the money up by increasing the cost of parts.
We recently had a Vauxhall Corsa 3 cyl and a Vectra diesel in on the same day both with Air Flow Meter faults. I can't remember the exact details but the Corsa one was around £240 and the Diesel one was aound £140. When they arrived they were both identical (Bosch Part Number F00C 262 030, Vaux No 961 27 2B), just the plastic pipe they fitted in was different. Out of interest I unscrewed both AFM's and swapped them over. Guess what both cars fixed.
I have since looked at various different Vauxhall AFM's and they look the same on most models. Perhaps somebody with more Vauxhall knowledge can confirm this and we can just find the cheapest one?