Hi Slomo,
The blow molded white plastic material and wall thickness of the material would not hold up for any length of time. White plastic fails with UV light, heat and extreme cold conditions in a very short time.
Example: I have older riders with the original "black" ABS tanks that are over 30 years old while all of the "white plastic" ones have long since crumbled to fragments.
I don't agree with the excessive cost of the OEM, but that is what the industry has become. Parts are exceedingly high to intentionally steer consumers toward buying new replacement equipment.
A complete cheap push mower can cost $300.00 dollar, but the replacement engine alone will cost $450.00 due to the mass manufacturing of "whole goods"/ complete mowers.
The manufactures are not interested in making/ supplying individual replacement parts or supporting repairs of any kind, there is no profit in that approach. Even the aftermarket suppliers have jumped on this money-making opportunity.