Rule Engine node does not support calculations. That why $column2$ * 100 won’t work and error is thrown. That is one of reasons Column Expressions node was introduced in KNIME. It is based on JavaScript syntax which is not that complex. Especially for simple IF statements and someone who knows Python
Considering your use case I would say you want to use Switch Statement. Link also provides good JS tutorial.
Alternatively you can use Rule Engine but only to output amount by which you need to multiply (100 from your example) and after that use Math Formula node to multiply two columns to get desired output. Python is one option as well but in this case I wouldn’t go that way.
In KNIME menu go to Help/Install New software.
On the form Input Column Expression and choose in Work with drop-down --All available sites --. Then follow the wizard.