You have to have a clue to port heads. Juiceman pretty much said it "stock heads work well if you know what you're doing".
TFS TW heads are about $1000, you don't have to do anything to them and they will outflow ported stock heads. You can have them ported later and get even more power. Same with Edelbrock or Holley.
$1000 dollar heads that work are a much better value than butchered $400 heads. Oh, and aluminum heads are about 60-80 lbs lighter than stock heads.
If value is the most important thing to you, are your current heads so bad that you can't just have them rebuilt and ported?
------------------
351W 89 Mustang GT Convertible