If the Internet is to be believed, $100 in 1909 would be almost $3,000 today. From the Skidmore New Era (Skidmore, Missouri), January 21, 1909, p. 7:
Good farms around Skidmore are now selling for $100 an acre and over. We hear every few days of a farmer who sold out here for $40 and $50 an acre, and went to Kansas or Nebraska and bought land for $25 and $30 which is now worth $50, and thinks he has done well, and he did, but think what the farm he sold here is worth today. It is hard to beat northwest Missouri.