As noted by @mattdm, part of your question is answered before:
But it seems that you don't have a good understanding of the whole concept.
An advantage of a DSLR is that you can use it with many different lenses, there are lenses with high zoom ratio.
Picture above is NIKKOR AF-S DX 18-300mm f/3.5-5.6G ED VR, it has the highest zoom ratio in Nikon lenses, that is 16.7x (300 / 18)
But there are other lenses, with more magnification and smaller zoom ratio. for example, NIKKOR AF-S NIKKOR 200-400mm f/4G ED VR II with only 2x zoom ratio is much longer than NIKKOR 18-300 (above) and more expensive.
Also some lenses come with a fixed focal lengths, such as the Nikkor 14mm f/2.8D AF ED which is wide lens on DX cameras or the recently announced NIKKOR
800mm f/5.6E AF-S FL ED VR which is the longest lens in the NIKKOR lineup. a prime lens has a fixed focal length and angle of view, and there is no zoom to play with.
To have a better understanding of different focal lengths, I suggest you to check this NIKKOR Lenses Simulator, there you can choose different lenses and bodies. as you may know, D300 is a DX camera, which means it has a cropped sensor, on the simulator you should choose DX body with either DX or FX lenses.
If you need a camera with high zoom ratio at an affordable price, take a look at Nikon COOLPIX P510 or its newer version, Nikon COOLPIX P520, they both offer 42x optical zoom, their lens is similar to a 24-1000mm lens in 35mm (FX) format cameras.