Wrong. He asks four and five dollars for a straw hat.
Right. He asks four or five dollars for a straw hat.
as. Use because as a causal conjunction rather than as.
Bad. I could not go to the game as I had to get the dinner.
Better. I could not go to the game because I had to get the dinner.
Use so after a negative rather than as.
Bad. He is not as bad as he is painted.
Better. He is not so bad as he is painted.
as though. As if is preferable to as though.