I've always wanted to have a go at a hot wire anenometer. I presume they work by the cooling effect of the wind changing the resistance of the heated wire? Gets around all the mechanical and weather-proofing problems?
Apart from that, I'd:
1. If it's for the fun/learning experience, try the slotted/disk method.
2. If you want it to work properly, outside and for a long period - byte the bullet and purchase the Davis sensor at about $125.

Regards Bill Legge