Since cup anemometers contain moving parts, such as bearings, and are likely to be subject to adverse environmental conditions including exposure to heat, cold, rain, ice and sand, attention should be placed on understanding the component design (including bearing, housing and shaft materials, lubrication, seals, etc.) and the use environment to ensure that the correct device is chosen. Attention should also be given to preventative and corrective maintenance.
I reviewed several sources such as NPRD-2011 and did not find any reported information on cup anemometers.
A brief web search on anemometers was performed and found service life and/or MTBF, as advertised on the data sheets of several manufacturers, to be somewhat varied. Two manufacturers advertised a 5 year typical service life before recommended replacement of bearings. One of the designs contains Teflon bearings and a hardened beryllium shaft, and the other contains low friction ceramic bearings, lightweight stainless steel cups, and an anodized aluminum housing. The sensor was also designed to prevent entry of moisture or dust into the upper bearing to prolong life. A third manufacturer advertised a 3 year warranty on a design containing stainless steel bearings and an anodized aluminum housing. Still another manufacturer advertised a MIL-HDBK-217F prediction of 2.34 failures per million hours in a Ground,Fixed environment. It is unclear if this calculation considered mechanical components such as the bearings. It did state that the ball bearings and sensor shaft should be checked annually and that the sensor accuracy was guaranteed for 1 year under all conditions and for 2 years under typical atmospheric corrosion conditions.
Given this variability I would suggest contacting the manufacturers that you are considering to use and attempt to obtain pertinent reliability, maintainability and service life information from them.