Kolakoski

Score: 94.25 (pass)

#!perl
($a,$b,$c)=@ARGV;for$i(0..$c){pos=$i;/./g;$_.=($i%2?$b:$a)x($_==1?$b:$&||$a)}print/(.{$c})/,$/

Score: 105.26 (pass)

#!perl -l
($a,$b,$c)=@ARGV;for$i(0..$c){$n=$i%2?$b:$a;/.{$i}(.)/;$t=$_==1?$b:!$i?$n:$+;$_.=$n x$t}print/(.{$c})/

Score: 134.28 (pass)

finally...

#!perl -l
($a,$b,$c)=@ARGV;for$i(0..$c){$n=($n==$a)?$b:$a;@t=($i==0)?$n:$l=~/./g;$t[$i]=$b if(length$l==1);$l.=$n x$t[$i]}print substr$l,0,$c