Doing the math for a command word item of CL 1 Unseen Servant that doesn't have charges.
1st level spell x caster level 1 x 1,800 = 1,800 gp
Just make it continuous use and let it be 2000gp. My characters usually have a broach or double the cost and it doesn't take up an item slot.
What do you want it for? Just curious.