Say, I want to compile a list of ork goods and use them to determine the cost as in how many teef they are worth.

As of right now we know that

• 1 toof - a good squig pie and a tankard of fungus beer.
• 2 teef - a decent weapon like a Shoota.
• 20 or more teef - a Warbuggy

So, how would other weapons like a power klaw, a high quality ramshackle eavy' armor or a kustom blasta worth? As far as I know, battlewagons are worth at least 100 teef.

Because just an acquisition roll to gain item from orks aren't quite logical, since most of the time nothing but teef and weapons/armor is worthless to them, so it wouldn't matter if the RT has a flow of billions of throne gelts. I would imagine that in addition to an acquisition roll, you would also need to provide an amount of teef to pay the mek.

You could always just provide him with a pile of scrap metal that you say contains the parts necessary to build "Da Biggest Shoota eva", and laugh as he trades you what you were after in exchange for some useless pieces of sheet metal.

You might stop laughing when he actually builds it, but hopefully you will have left the area by then.

Since I'm the GM, why would I want to feed the player free stuff for no reason?

Depends who the Mekboy starts testing his invention on. I recommend that group of 'umies that thought they were smarter than him.

Since there is no hard-and-fast rule it is also the job of any GM to look briefly confused, and then explain that since the Rules As Written don't cover this the plan your players came up with didn't work but don't worry, you have an idea that will let them go through with this plan and then make them go through something excrutiatingly difficult as punishment for trying to sequence break.

Or we can try to be Scientific about this (I think that's a heresy)

A good squig pie and a tankard of fungus beer equates to a mid-grade meal, which is of Common rarity.

A "decent" weapon like a Shoota equates to an Autogun, which has a of Average rarity.

A warbuggy is probably one step rarer than a Warbike, which is Scarce rarity so we'll put it at Rare rarity. Vehicles are automatically more difficult to acquire, so let's make it Very Rare.

Now that we have some data point we can try to fil in the rest of the rarities.

Common - 1 Toof

Average - 2 Teef

Scarce - 5 Teef

Rare - 10 Teef

Very Rare - 20 Teef

Extremely Rare - 50 Teef

Near Unique - 100 Teef

Unique - 200 Teef

Now you just have to set the rarity for the item you want from the chart and translate into this (with a bit of haggling thrown in).

Power Klaws are Near Unique according to the Koronus Bestiary, so those will be 100 Teef.

High Quality Ramshackle 'Eavy Armour would be presumably be the equivalent of Best Quality for Orks (Buh?) and thus from Rare to Extremely Rare, or 50 Teef.

Kustom Blasta would involve taking a Blasta, and paying a Mekboy to "build" the upgrades as given in Into the Storm.

See if this works as a starting point.