There's a Quality Inn right across the street but if you are looking for someplace inexpensive...
Niagara Falls Blvd has $20-$30 motels for tourists,etc... along the boulevard (15 minute drive from airport)
If you want to stay in close proximity - you would make a left on Genessee (where the airport is) and then take a left on Transit rd (about 1 mile down from airport) and theres a bunch of cheaper ones.