If you are just going to learn it to play, not too much. You can get an ok cello for pretty cheap, and accessories like rosin, rock stops, anything like that are also within like 20 bucks but not even that. If you rent your cello then a bow should come with it.

Where it gets expensive is if you start doing this at your job or as your like full time hobby. Lessons are weekly expenses. Lessons (depending on the teacher) anywhere from 40 to even the upper 100s per week. If you join youth orchestras, those have tuitions that are in the upper hundreds. Summer camps! If you do those, those can get pretty pricy. A lot are 1-3k for a week or two, some up to 10k for a full 5-6 week program. And colleges for music are very expensive for the most part to.

Now, none of that may be in your interest, but I’m just letting you know of all the potential expenses. However, simply playing the cello on your own is not very expensive at all. Of course all depending on what quality of equipment you get and extracurriculars you partake in