I've read somewhere of feats that allow you to craft wands and potions of up to level 9. I"m pretty sure they are in 3rd party books though (not form WotC). They use the existing item creation rules its just a couple feats that allow you to create wands with spells 4-6, then another feat for wands 7-9 and the same with potions.
In general the following formula works fairly well for creating items based on unlimited usage of spells Spell level x castor level x 1500gp. So if you have a 4th level spell you want permantly enchanted on an item (such as inflict critical wounds) it would 4 x 7 x 1500gp=42,000 gp to enchant an item so that it has limitless charges (spell rules still apply). Other considerations may apply to this rule based on the spell you want to use and this isn't an exact science. Its a good estimate and starting place for creating magic items. Please consult the DMG for complete rules on magic item creation and look for other similar items to compare pricing or to get an idea of how to price items.