Inspire Greatness (Su): A bard of 9th level or higher can use his performance to inspire greatness in himself or a single willing ally within 30 feet, granting extra fighting capability. For every three levels a bard attains beyond 9th, he can target one additional ally while using this performance (up to a maximum of four at 18th level). To inspire greatness, all of the targets must be able to see and hear the bard. A creature inspired with greatness gains 2 bonus Hit Dice (d10s), the commensurate number of temporary hit points (apply the target’s Constitution modifier, if any, to these bonus Hit Dice), a +2 competence bonus on attack rolls, and a +1 competence bonus on Fortitude saves. The bonus Hit Dice count as regular Hit Dice for determining the effect of spells that are Hit Dice dependent. Inspire greatness is a mind-affecting ability and it relies on audible and visual components.
So if you wanted to make a magic item that does this to yourself how much would you say it would cost?
I am a fan of custom magical items. If priced and applied properly, I find that these items help make non-casters keep up with casters (especially in the utility department) while also giving casters more flexibility in how they choose or prepare spells. I find that minor items like "spectacles of Comprehend Language" or a"Ring of Air Bubble" can be fun and very popular with my players without upsetting the balance of the game.
Keeping that in mind, I would not allow an item like what you describe in my games.
Bards get unique buffs because that is a big part of their 'niche'. Allowing defining class features to be added to items dilutes what makes the classes unique.
I also wouldn't make an Item that replicates a class feature, takes away thew poor Bard niche.
If y really insist on making such an item, you might consider "The Lord's Banner(victory)" from the APG as a reference Item for pricing your Item.