C:835

There's already a heavy version:

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BLADED CROSSBOW (Magic Item Compendium, pages 47-48)
Price (Item Level): 4,660 gp (9th)
Body Slot: — (held)
Caster Level: 11th
Aura: Moderate; (DC 20) evocation
Activation: —
Weight: 12 lb.
The front of this heavy crossbow is fitted with a pair of curved, sharp blades. The gap between them is perfectly positioned to allow the unhindered passage of a crossbow bolt.

This crossbow has an exceptionally strong stock, which is shaped so that you can grip and swing it as a melee weapon. You can use a bladed crossbow as either a +1 heavy crossbow for ranged attacks, or as a +1 battleaxe for melee attacks.

Prerequisites: Craft Magic Arms and Armor, blade barrier.

Cost to Create: 2,000 gp (plus 660 gp for masterwork heavy crossbow and masterwork battleaxe), 80 XP, 4 days.


I guess a light version could be treated as light crossbow/handaxe and weigh half as much.