How much to tip contractors' workers?

We are moderately renovating a weekend house on Long Island — adding lighting, ceiling fans, switching out a bathroom vanity and flooring, making some closet modifications, taking out a second kitchen and painting the interior. A team of 5 to 6 men is working at the house for about 2 weeks. How much should I tip each worker? I asked the contractor and he said that people tip whatever they can afford. He wouldn’t be more specific even when gently pressed. So I turn to you, oh wise Brownstoners. What would you recommend is an appropriate amount to each employee? FWIW, the company owner’s son is the foreman. Thanks in advance.