1. All spellcasters are assumed to be able to craft items appropriate to their specialty, even pure Evocation users (though theirs would be limited to appropriate evocation effects and Focus Items for Evocation). A Pyromancer, for instance, can totally make a Blasting Rod or an Enchanted Item that sets things on fire...he just can't make Items to do anything non-fire related.
2. Personally, I'd allow such a character to take Refinement for extra Item Slots at no downside. it's hardly spectacularly unbalanced, after all.
3. Look into Sponsored Magic. Some specific variation of that is likely the best way to build the effect you refer to, and not any more expensive than what you're talking about.