Asking this question on behalf of my brother.

He has been using his old 80GB HDD as OS drive (split into 2 partition, 71GB actual size + 3GB as page file)
typically he use up like only left ~7-8GB free space

what size SSD should he get? prefer to spend as low budget as possible as he know SSD will still have a lot of room to drop. Using SATA III

90GB/96GB = what is cheapest in market?
120/128GB = what is cheapest in market?

main concern here is reliability, price, capacity. Speed is not the concern.