Here are some suggestions:

Plaza Motel
Chateau
Peeks Motel
Bikini Beach
Flamingo Motel

Some of which can be found here:
(also try Counts Oakes Resort Properties - you can search their website for available condos and rentals)
TripSmarter.Com: Panama City Beach/Accommodations

Also, try our hotel price comparison... lots of rooms for under $100 here:
Hotels in The Panama City Greater Area, Florida