i had mmr ported pi heads on my last stang. with new bronze guides, time serts, springs, new stock valves, lock retainers, seals it came out to 1200 dollars, re-using my old heads. not sure if this is much help but when i sold my car i swaped my fuel system to my cobra and the car made 458 rwhp with a built motor, 9.5-1 cr, stock cams, 3.33 pulley, intercooled and meth @ 5500 rpm's. car maxed the fuel system so its not done getting tuned.
out of the box tfs heads out flow the fox lake stage 3 pi heads ,, i have a set of the 38 cc tfs heads on my car and for the money they are a bit over rated but are verry nice and have a lot of good featchers like replacable cam towers, you can run big cams with no problems and they all ready come with good springs valves and so on,, i dont know how mutch power they gave me , i added them with 270 cams and the eddy intake and the car make a lot of power over 4000 rpm and i dont have it tuned yet, some day i plan on swapping them over to my 5.4 build im shure they will shine more on that set up
but there is more to head flow numbers than peak as well. tfs will flow more than almost any ported pi head out of the box, unless you get some from a select few places that can get the flow from the pi's. you also have to remember you are working with a 3.55in bore as well. i am hoping to get mid 240's out of my heads when i am finally done with porting.
There is more to consider in buying the TFS heads other than the flow numbers. The repositioned valve give more PTV clearance. You have two choices in combustion chamber volume, and the cam towers are replaceable if you mess one up. Even in terms of flow numbers bigger isn't always better. You can seriously hog out a set of heads and get huge flow numbers but you could also kill the air velocity which ultimately hurts performance. So even if ported PI heads match the TFS heads in air flow they may not be better.