"In hand" is the correct answer, but I think "on hand" is also okay here. When you have money in hand, it means you have the money with you (whether it is actually in your hand or not), and you are ready to buy anything at the moment right away. When you have money on hand, it means you have the money, but it may still be in your bank account or at home, etc. You could spent it, it is somewhere where the money is available for you to get in little to no time at all.

None of these would be correct in this context. We can say 'close to hand' which means something is near you, handy. We can also say that something is 'at hand' - also close to you or meaning that the time to do something is now. "The time for action is at hand.' But you couldn't use these with 'money' as in your example.