These were extrapolated from the siege weapons from the DMG by Eric Ingalls...
Weapon-------------------Dam--Crit----ROF----Crew---Cost
Ballista, Light-------------2d6---X3-----1/2-----1--------400 gp
Ballista, Medium----------3d6---X3-----1/3-----2--------600 gp
Ballista, Heavy------------4d6---X3-----1/4-----4--------800 gp
Ballista, Dual Light-------3d6---X3-----1/3-----2--------800 gp
Ballista, Dual Medium----4d6---X3-----1/4-----3--------1,200 gp
Ballista, Dual Heavy------5d6---X3-----1/5-----5--------1,600 gp
Catapult, Light------------3d6---X2-----1/2-----1--------500 gp
Catapult, Medium---------4d6---X2-----1/2-----3--------700 gp
Catapult, Heavy-----------5d6---X2-----1/3-----5--------1,000 gp
Bombard--------------------3d6---X3-----1/3-----3--------20,000 gp
Bombard, Great-----------3d12--X3-----1/3-----5--------60,000 gp