L series hold their values well.... unfortunately unless you own one ....Like stated above you don't have to spend a fortune for good pictures. Mirrorless or mirrored isn't going to make a huge difference it really comes down to lens quality. A good piece of glass can produce great images on a less than ideal camera body. The most import things are knowledge of the equipment you are using and how to adjust exposure. If you are not locked into the nikon mount Id suggest a canon and get a used L series macro lens.