My considerations in buying land through the years has been in order of priority:

1. Can I borrow the money.
2. Can I make the payment given average yield and prices based on my guess what they will be. 
3. If I am wrong on item 2 and come up short will my public job make up the difference.
4. Is it land I have on my short list for land I really want. 
5. Is the price anywhere near what I consider reasonable. 

Never really considered crop prices and interest rates at that point in time.  Looked more at gut feel over what they would be over an extended period of time.   :