Hey. I would say 'I really really want to come in to see you but... I really really can't afford it. I'm sorry'. Now... I do have a tendency to apologise more than is helpful, so maybe the 'I'm sorry' is unnecessary... But I guess I would say that. It is being honest about your situation. And it is up to your therapist how to respond to that.

If they simply can't see you then I guess they won't...
But it might be possible that they can.