Is the agreed-upon price of the land to be paid at the time of signing the contract, or at today's price, despite the seller signing the contract and refusing to take the money?

The seller's failure to collect the price does not invalidate the sale or affect its validity. As long as the brother agreed to the price of 250 per meter, he has no right to reject the sale. The sale is binding, and he is entitled to his share of the price. This is unless he claims that he was subjected to an excessive ghabn (deception/fraud resulting in severe loss) and was unsuspecting (mustarsil), in which case his claim should be investigated. Excessive ghabn is determined by the custom of merchants, or if it amounts to one-third or more of the price. If it is confirmed that the deceived party (maghbūn) was unsuspecting and the ghabn was beyond what is customary, then the deceived party has the option to either annul the contract or uphold it without any additional charge.