So you may have seen these in "action" in my most recent hireling post - my house ruled crossbow weights. GURPS Low-Tech covers crossbows in greater detail than this post does - you have rated strength and materials and a variety of implements to use with or to span crossbows. I wanted something simpler, so I updated a size/cost differential from my old GURPS game to the heroic scale of my DF game. If you want realism, go to Low-Tech. If you want heavier crossbows, with simple numbers picked out of the air that feel okay, this is for you.
First, use only the crossbows on the weapon chart in Basic Set. The rules below replace those in Low-Tech, and are not compatible. Combining them with get extremely odd effects.
Crossbows are available in four broad draw strengths:
Light Crossbow: ST less than 10, normal cost, 2/3 weight ($150, 4 lbs)
Crossbow: ST 10-18, normal cost and weight ($150, 6 lbs)
Heavy Crossbow: ST 19-28, +1 CF and +50% weight ($300, 9 lbs)
Siege Crossbow: ST 29+, +3 CF and double weight ($600, 12 lbs)
All of these are changes to the base cost and weight.
Available accessories include those in DF1 (crossbow sling, brace, sight), Basic Set (goat's foot), and the stirrup and cranequin (from Low-Tech p. 79). No other accessories are available, regardless of TL.
Composite Crossbow - A crossbow made out of lames of different materials for a better bow. +1 damage, +5x to half damage and max range. +9 CF. (Makes a normal crossbow $1500 but thr+5, x25/x30)
Steel Crossbow - A crossbow made out of metal instead of wood. +1 damage, +4 CF, +50% weight. Cannot be combined with Composite. (Makes a normal crossbow $750, 9 lbs. but thr+5)
Light crossbows cost and weigh as much as pistol crossbows? - Yes, but they require two hands, yet have better accuracy. It's a tradeoff.
What's the Max ST of a crossbow? - I cap them at ST 40, which is 4d+1, because beyond that I think it's overlapping siege weaponry too much. I just say you've reached the limits of materials and size before you need a mount and a much larger bow, making it impractical for hand-held use.
Does this apply to prodds? - Yes.
So the most I could get is . . . - A ST 40 siege crossbow, made of metal, for $1,200 and 18 lbs. doing 4d+6 impale or 4d+6(2) pi, or more with Fine bolts and Puissance, or a ST 40 composite siege crossbow for $1,950 and 12 lbs, doing 4d+6 impale or 4d+6(2) pi, half damage range of 1000 yards!*
* I did a guy just outside Felltower, once, at about 1,000 yards . . .