Bf needs adhd meds, gp said talk to a psychiatrist for evaluation. how does that work? how much is that evaluation gonna cost without insurance?

Most urban cities: have free mental health clinics subsidized through the public health system. Do a little research for yourself locally and I suspect you can obtain the evaluation and treatment at no or at least very reduced cost. When dealing with issues like ADHD in an adult it is important to be evaluated and not just given medications without evaluation. The GP made the correct recommendation.