The answer to this first question is very clear while the answer to the second depends a great deal on the specifics of the case.
In the first question, it is clear that the Krauses cannot void the contract unless it is found that Jud in some way acted illegally towards them. A contract cannot generally be voided because one side simply made a bad deal. In order for the contract to be voided, there has to have been fraud, duress, or undue influence. If Jud lied to the Krauses in some way (for example, if he falsely told them that he was a geologist and their land was worthless because it was prone to landslides), the contract could be void. If he told them that he would kill them if they did not sign, the contract would be void. But if he did not do anything like that, the contract will stand. You cannot get out of a contract simply because you find out that you made a bad deal.
In the second question, the issue is less clear. In general, courts rule that a person who drafts a contract is responsible for the mistakes in it. So if Jud writes the contract and accidentally writes in a higher price, it is his fault and he must pay that price. However, if the price he writes in is completely ridiculous, a court will probably not hold him to it. So, let us imagine he meant to pay $40,000 and he typed in $45,000. The court will probably force him to pay the higher price. However, if they agreed to $40,000 and he typed in $400,000, the court will probably rule that it was obvious that that was a mistake and so he will not be held responsible. However, it is hard to know how big the mistake has to be before the court deems it ridiculous.