How to buy the plane?
Solution 1:
The honest answer would be waiting just as long as it takes for you to be able to afford 100 new mining machines, buy them, wait again etc. until the time required to obtain the (now) 5e6 ironbars for the plane.
The cheating answer is, open a JavaScript console and enter ironbars = 5e6
Solution 2:
(I literally wrote this answer like 50 min ago on a different post) To get extra iron bars (or anything) in The Gold Factory, you would need to edit the save game code. Do this by changing the decoding the base 64 save game code. You can use this website. https://www.base64encode.org/ The second number after the decryption should be the number of iron bars you have, while the first number is the amount of gold bars you have. Change that, then encrypt the code again. Add "encrypted" to the end of the code, and there you go! Here's my code:
MTAwMDAwMDAwMDAwMDB8MTAwMDAwMDAwMDAwMDAwMDB8MTZ8MTYwfDMzfDYwfDEzNHwwfDJ8MXw1OTB8MXwxfDF8Mjd8MXwwfDB8MHwwfDB8MHwwfDB8MHwwfDB8MHwwfDB8MHwwfDN8MHwxfDN8NHw0fDF8MnxZb3V8VGhpcyBpcyB5b3UufDB8MHwwfDB8ZmFsc2V8ZmFsc2V8ZmFsc2V8MHxmYWxzZXx0cnVlfHRodW5kZXJ8NXwzfDF8MTd8ZmFsc2V8MHw5OTk5OTk5OTl8OTk5OTk5OTk5fDB8RGlhbW9uZCBTd29yZHx0cnVlfHRydWV8dHJ1ZXx0cnVlfHRydWV8dHJ1ZXxmYWxzZXxmYWxzZXxmYWxzZXxmYWxzZXxmYWxzZXx0cnVlfDV8ZmFsc2V8dHJ1ZQencrypted