Dad is obsessing over finding out cost of nursing care. What do I tell him?

My dad is in a nursing home and is lucid and conversational sometimes. He has lived a very frugal life and has always been obsessed with how much things cost. Lately he has been obsessed with how much it costs to stay that the nursing home and is determined to get to the bank to see what checks have been written and how much money he has in his account. I've tried to reassure him that I am taking care of everything and he has plenty of money. His girlfriend and I keep evading his questions. She keeps telling him she can't take him to the bank because she can't manage the walker/wheelchair. Now he is asking other residents how much it costs. If someone tells him, I don't know what will happen. Yesterday he managed to convince the staff his girlfriend was taking him to the bank and they actually started making arrangements with the social worker, head nurse, PT. I was shocked. They support patients being involved in their care. I've talked to the social worker about this and her advice has been to tell him what he can handle at the time. Not helpful. The cost is mindblowing. Do I make up a number? If I do and he hears otherwise, trust is broken. How do I get him to stop stressing about getting to the bank? I just don't know how to handle this. I am sick by the size of the checks I am writing. I've explored other options but he needs this level of care. I've been told by a friend who has gone through this that this type of questioning never ends. It is behavior consistent with his personality and we are stressed to the max with this (combined with everything else of course). Advice? Thank you in advance.