I've commented numerous times before on this board about "cheap" hotels, but will refrain from doing that here only to offer an opinion. I would imagine that this is a very slow time for Orlando. Scholl in in full swing and summer vacations are all but over. So I would think these "signs" may be there to attract those few who are travelling through Orlando and have not made any hotel reservations. You should see things pick up again just around Columbus Day (mid October) and the end of November.
Ok... so I can't resist. I would imagine the "$19" hotels are the ones that usually charge about $39 a night, which in that case, I would NOT chance staying there anyway. I suppose if I were driving back to NY from Key West and this is as far as I could get before needing to sleep (highly unlikely), I'd check out the room first and plunk down the 19 bucks for a night's rest