And the real cost of manufacturing is not from the genetic adaption of the cells and their growth, but is in the purification. After the cell has replicated and grown all the protein (Mol wgt 3,000 - 15,000) you want, you have to extract it from the chemical soup that exists in the cell. The cells are ground up and then filtered physically and chemically to separate out the one protein you're interested in. With antibodies the situation is often more complex because of there extreme uniqueness (which is what makes them such good drugs) and their size.
Also adding to the cost is the level of hygene required in the manufacturing plant. The slightest infestation of mold or a failed test for bacteria in the factory can shut the manufacturing down for 3 -9 mths to clean up and sterilize the working environment.
So biosimilars get cheaper because there are fewer clinical trials (usually just for safety issues) but the manufacturing is still way expensive compared to small molecule (mol wgt 300 - 500) chemicals