From my own experiences Diamond hammer with 3x3 AoE, Damage 8 (which is the minimum needed to one shot tier 6 rock), Speed 4 (which is pretty low, not sure why your aiming for this level?) would probably be at around 8-9k
A similar hammer with Max (10) Speed could probably go 10-12k easy
Anything over 15k is getting quite expensive even for perfect forges (for non-exo gem stuff) IMO
Everyone has their own ways of forging, but generally if I cant get atleast damage 8 and speed/durability 6 with 3x3 aoe, i just use deconstruction resin and try again, which gives back 75% of the used forge materials + the unforged tool (when using level 3).
But then again, i also never use roadrunner feathers because of their cost, so its personal preference.
Original forgeries in Nova Golda on trung has hammers for between 8-9999 depending on stats. T5 , quirk and alloy tools are cheaper. Alloy typically 1999
I pay 12k for perfect hammer and see that kind of price consistently around a few shops I check. I managed to buy such hammer for 10k a few times but 12k I accept as fair enough.
I sell 4/10/10 (aoe/damage/dura) no quirks or defects for 12k I believe. Haven’t been to shop in couple days. So anything more than 12k if not max non quirked/defect to me is overpriced.
It all depends on the gem tool and stats. 1 month ago I bought 110+ diamond hammer with t6 damage, 3x3 and between 1400 to 2000 durability for prices between 6000 and 9500. 9500 is imo already higher end pricing but had 2000 durability and was happy with the service + it went to a nice person