How much should I sell my used Nikon D40 for?

I have had it for two years now - the body itself is in perfect condition, no visible marks or scuffs. The 18-55mm nikkor lens that it came with does have a couple noticeable scratches/scuffs (which may come off if cleaned professionally) on the surface but they do not show up when pictures are taken - also on the lens, the sticker that lines the inner part of the lens which displays the measurement of the lens itself is no longer there, and there's residue from the sticker but it does not affect shooting. At times when shooting photos, the lens makes a clicking sound as if it has become unattached and the picture through the viewfinder appears to be unfocused - quickly detaching and reattaching the lens is needed to continue to take photos.
An estimate of a decent price is $300 for both the lens and body - is this reasonable? I also have the original box, charger, and "quick start" manuel.

That having to take the lens off and then re-placing it to take a photo makes either the lens or camera body defective and that will really draw down your asking price. Because something is going to have to be repaired or replaced.

What's the shutter count? Can you get that? If so post it with your sales announcement.

I'm not really familiar with Nikon but if I understand correctly the 40 is pretty old. So what's the sensor's MP count? - 8mp, 10mp, what?

Given that either lens will have to be replaced or the body repaired to elevate that problem you mentioned about removing the lens, I'd think your starting price should be no more than $200.

Sell it for soggy peanuts.