It looks like right now you are shooting with the D80 and a 18-55mm f/3.5-5.6G. Something in the D3000 or D5000 series would be a similar crop-frame camera and compatible with your current lens. In Nikon generally the higher the number, with the exception of the first digit, the newer the camera. For example, the D3600 is newer than the D3400, but may or may not be newer than the D5500.
B&H has a large selection of used and refurbished, as does Adorama. Both are in NY city, but are also huge online camera stores with great reputations.
If your budget allows, do not skimp on the lens you pick. A general rule of thumb I heard once is, to get the best quality photos for the price you should get a lens that is worth as much as your camera body. If you get a prime lens (no zoom) that might not apply, but for a general zoom, I would tend to agree. For a D3000 or D5000 series you will want to make sure there is a focus motor in the lens. Full-frame lenses work on crop cameras, but not the reverse.