And why would they sell you land for less if they know you have $40k more of income? Everyone can pay that extra money, if I am a seller I am raising my prices accordingly.
Is there a reason other than naked greed, why you (philosophical 'you', not you personally) would raise your prices accordingly? Keep in mind that even as a multi-millionaire slumlord you would also receive UBI (or else it ain't universal) which is enough to cover basic food and shelter.
Because you don't directly set real estate prices based on the buyer's income. You simply sell to the highest bidder. The bidders look at their own income and decide what to pay. If all the bidders have more money, the price will tend to rise.
And why would they sell you land for less if they know you have $40k more of income? Everyone can pay that extra money, if I am a seller I am raising my prices accordingly.