I looked into safe cracking a while back and it seems most of them are sustainable to various attacks. Instead of spending a dime on what's most likely empty safe i would make it a funny family hobby to try to break it. If they have no use of the safe afterwards i would apply more brute force, seeing they are not limited by time. Drilling a hole and inserting an endoscope would be a fast solution, but would ruin the challenge of breaking it :)