Need some help with pricing of magical weapon

[Lavranzo]

So, I've made this magical sword which is described beneath, and I need some help for the pricing (if a pricing is viable here, and if not, how strong compared to say a weapon +x would it be?).

Sword of the berserker
Worth: ??? GP

The holder can alter this bastard-sword’s size at will. Normally around 1 meter in length, and 4 cm in width, the sword can be resized to as much as three times its normal size. No matter its size, it will always feel to the bearer as light as a normal bastard-sword.
Maximum size: 3 meters length, 12 cm width.
Its damage changes accordingly; ((1d10 +2 per size factor) + other bonuses)
Maximum damage: 1d10+6 (+ other bonuses)

Any help would be appreciated.

[Glimbur]

Normally, weapons of different sizes do different damage like so. It works out pretty similar to +1 at the smaller ranges, but once you are at 1d8 the increases get bigger.

There's a 'sizing' weapon property in the magic item compendium. It costs a flat 5000 gold and lets you change the size of the weapon freely. This is nice but pretty niche; sometimes you change size via polymorph or whatever but it is probably not worth even a +1.

So, I guess my answer is that WotC already did something similar in first party. If you're looking for a weapon that gives +damage then you can compare it to enhancement (+1 to damage per +1 of enhancement) or the elemental brands (+1d6 damage for +1 equivalent, but it's elemental which can be resisted). Or to collision, which is +5 damage for +2 equivalent. I think those options cover what you are looking to do?

My favorite and least favorite thing about 3.5 is that there are a bajillion books for it with ten bajilliion rules. It lets you create many different concepts but it is a lot to learn.