My camera? Well I guess you could get a camera like mine for anywhere from 50 € to 350 € used, cheaper if you are lucky.

My advice is that if you are really interested in photography, practice with what you've got and save money, until you've got enough. Then get yourself an affordable camera body with a good range of lenses available. (Doesn't really matter what brand it is as long as there is a good lens selection available.) You will often get a cheap kit lens with it, but it's also advisable to invest in a good 50 mm prime. You can find those from 50 € used to 150€ new.

If you want to shoot the moon on a budget, a Sigma 70-300mm seems to fare pretty nicely against a newer version of the Canon EF75-300 I have.

If you are serious about star photography I have no experienced answers as what to invest in, only guesses. I'm thinking of investing in a 150-600mm lens might be an option. What brand exactly I have no clue, but I guess the prices can vary from 1000€ to 3000€ depending on the quality of the glass.

And then there's this:

Canon EF 1200mm f/5.6L USM for just under 100 000 €

One can always dream, right?

Anyway, choose a good lens, not just any lens. Keep in mind that there are lenses for full-frame cameras and crop-sensor cameras, and while the full-frame lenses work with cropped cameras, the reverse often doesn't work and you will end up upgrading the lens if you ever upgrade the body.

As you learn to shoot photos, you'll come to the point where you may eventually want to upgrade the camera body. At that point you'll probably already know which way you want to go and invest in a camera that suits your needs as a photographer. And the lenses you've already acquired will likely work with the camera body you choose. If you go from a crop sensor camera to a full-frame, you might have to upgrade some of those crop sensor lenses too though.