I agree 100% reduction cost although awesome you have the ability to do it... It just wouldn't be fun for me. The ritual stone... Interesting, so basically I should avoid tangible weapons? The frost (or lightning maybe idk?) destruction magic tree will be sufficient for defense?
You could always use summoned weapons, although for them to truly be effective you'll have to dabble in a weapon skill, like archery, or one hand. When I think Necro, I think no weapons, except maybe a Mace for last resort situations, or maybe a dagger. But that's like a last line of defense situation. I chose Lightning over the others since my pure mage uses frost and fire, and lightning seems 'powerful and evil' for lack of better words, but you can do whatever, hell, use all three elements if you want. I just like making a lot of builds so I limit myself since there's no more spell creation and magic gets boring after 2-3 builds.