Not so sure about "cheap" -- I think the fan I'm thinking of cost me $13.
It is a "tip-magnetic" fan, and I forgot the name of the manufacturer. It is -- indeed -- 70x15mm, very quiet. Since there is no "motor assembly" at the hub, it has higher than average airflow for fans that size -- the hub is rather small.
Check the specialty houses -- FrozenCPU, CoolerPC, Jabtec, Performance PC, CrazyPC, Sidewinder Computers, SVC, etc. and run a web-search on "tip magnetic fan."