By the looks of those exhaust ports, someone has already done some porting.

If you had an untouched virgin pair of castings....... By the time you buy all the parts, take care of the "usual" things that are typically wrong with those heads, do a valve job, bowl blend, flat mill and assembly........ It can very quickly add up to over $1000-1200.
That's if they don't have any of the more serious issues they sometimes have, and you don't have to replace the guides, and don't need severe duty parts installed.

The only "cost effective" way to have those heads done, and have the issues taken care of is to do much of it yourself.

It's hard to give an actual price on those things because without having them on hand to inspect, there's no way of knowing how good or bad a particular set is.
Some aren't too bad....... Others are a real mess.

Here's some numbers from a std stage vi with the CNC'd chambers option.
Ferrea 5000 series 2.14/1.81 valves. This is what you got ootb:

Lift--------in/ex
.100---67.4/52.3
.200--126.3/108.5
.300--181.3/137.7
.400--215.0/144.8
.500--235.0/149.1
.550--236.9/149.1
.600--238.8/149.1
.650--240.8/149.1
.700--242.7/149.1

Valve job, back cut, blend bowls:

Lift-------in/ex
.100---66.6/53.0
.200--151.2/123.6
.300--201.7/166.8
.400--242.6/178.5
.500--263.8/183.2
.550--260.0/187.0
.600--261.1/194.2
.650--261.1/197.7
.700--261.1/199.6

This is about what you can expect for mild prep work.
If you want to get into the 290+cfm range on the intakes, you'll have to do some real porting.

The head these numbers came from is one of the versions that had the really huge guide bosses. Some of the later versions had much smaller guide bosses, and those took less work to get the numbers up around 290.

I just looked through my notes......
I have some numbers from a set that had a date of 03/2005 on the box.
These had the much smaller guide bosses compared to the head the numbers above came from. It also had some rough carbide work done in the bowls.
I got 270/190 from that head ootb.......so they are definitely not all created equal.
Of course, I also see it was over 90cc chamber volume.