The Motel 6 in Seaside is clean and nice. If there is not a Monterey event going on, it's fairly cheap.

Martine Inn is a B&B, but it's a beautifully restored victorian, with very nice rooms. Light and airy. A high level of service, but very unassuming about it.

Monterey Bay Lodge was also very very nice. They claim to be upscale (and they are) but can't hide that they are very renovated motel.