I didn't hire a camera from them. They employed me and provided me a camera to work with. Big difference...
How?
If I hire you to shoot something for me, and I give you my camera, and you subsequently lose the lens cap... How is it my fault that the lens cap is lost? Why should I have to cover the cost of the lost lens cap?
You lost it.
Do you want to work with these guys again?
It's a lens cap, man - I can't see how you could possibly be paying more than around $80 to replace it. A still lens cap costs around $5 to replace; a Cooke mini S4/i lens cap costs around $40 to replace.
Are you really going to make that big a deal over that small amount of money..?
To be perfectly honest, I think it's
worse if you didn't hire the camera. If you hire it, you've at least traded some money or similar value for the hire of the camera, so a missing lens cap isn't so bad as you've probably paid much more than the cost of a lens cap to hire the equipment.
Instead, someone's paying you to do a job and you've
lost their lens cap, and you don't think you should be responsible for the replacement of it?
If you gave your camera to someone to shoot something and it came back missing a part, would you expect them to replace it?
If someone hired my camera, brought it back without a lens cap and said 'I'm so sorry man, I'm not sure where it is, feel free to charge me for it' I'd probably absorb the cost myself. Someone who argues with me, I'm going to want them to pay.