use php variables for awk regex commands

trying to implement autosuggest using php. autosuggest list generated using awk

    $input= $_GET["term"];
   $suggest=array();
   exec('awk \'BEGIN{FS=","}/.$input./{print $2,"-cost-",$1}\' 3.txt',$suggest);
   echo json_encode($suggest);

in place of $input to test autosuggest i was using a charachrecter eg.A works fine. however i am not able to take a dynamic character as an input to awk. some thing wrong with .$input. cant figure out how to write the escape characters

thanks in advance