Cheapest 120hz monitor i found on newegg was 250$
Ive had 120 hz monitors for about 2 years now and wont go back to 60hz.
I makes a big difference in first person shooter games such as counter strike source and battlefield 3.
I find when sniping enemy players that are running accross your screen is smoother and easier to do on 120hz compared to 60hz but thats my personal opinion.
I hope other OCN members will share their 120hz opinions.