Added missing costs to unique artifacts

It wasn't possible to transmogrify a couple of non-quest artifacts, this was due to them not having a cost value, which seemed like an oversight.

I reviewed the different world artifact and boss artifact Lua files. The affected items are:

• Crude Iron Battle Axe of Kroll
• Mummified Egg-sac
• Razorblade, the Cursed Waraxe
• Rungof's Fang

I looked at similar seeming items to determine the cost values.