A much less expensive option than a macro lens is a Nikon 6t close up diopter lens. They're discontinued and only available used. You would also need a step up adapter ring to fit it on the 50 or 18-55. The 6t has a filter thread size of 62mm. There are single element diopter lenses that are much cheaper, but the 6t will not degrade image quality like a cheap one will. Just remember working distance will be short with shorter focal lengths such as 50 or 55mm. here's a link.
Edited with the following: I see in your signature you have a Tamron 70-300. The 6t will offer more working distance and larger reproduction ratios with longer focal lengths, so it may work better with the 70-300. But in my experience, using the 6t with too long a focal length caused degraded quality. So maybe you can use it in the 70-200 range.