The Runes of Power are $30.00 each with no tax.
Same as all the Valkyrie weapons.
The highest priced items in the donation shop are the infernal capes, iirc.
The prices aren't all that mundane. I myself have donated a few dollars just because I have no time to farm.
It's all a matter of preference. If you have the time and patience to farm the gear yourself then kudos. If you're like me who doesn't mind spending a little but of dough on a game you like playing then donating isn't all that bad either.