Is it permissible to share with colleagues in paying a food bill that includes alcohol, knowing that what I pay is far less than the price of the halal foods they consumed?

As long as the amount paid does not exceed the price of the halal (definition) food, it is not considered a payment for alcohol. Nevertheless, it is not permissible to sit with those who drink alcohol, as this constitutes an endorsement of evil. Furthermore, participating in paying for the food is considered aiding in sin, for the Prophet, peace and blessings be upon him, forbade sitting at a table where alcohol is consumed. And whoever believes in Allah and the Last Day should not sit at a table where alcohol is circulated. Moreover, whoever sits with someone who violates the Sacred Law while they are engaged in that violation shares in the sin. Therefore, it is obligatory to abandon sitting with these people at their meal if it involves the consumption of alcohol.