How can i book SAM Guest house?

My relative is coming for a day or 2 and i want to get a room booked for him. TGH charges are really high. Heard that SAM charges are low. Please tell me the procedure for booking. And also i saw a notice on iit kgp site for booking a room in sbp1/2 or abv which charges only rs250. They haven't mentioned whether that notice is for the students coming for attending the fest or in general forever.