Astronomy as someone wrote, but some other hobby can have high ceiling, like RC stuff, radio control ; sure as long as you stay on the road you start with a 1/16 brushless car for a few hundreds and can upgrade to 1/6 2 strokes behemoths for a couple thousands. Some people are in rock crawlers and it can become expensive too even for a hobby. When you go in RC planes, first the radio goes from a simple 2ch one to a computerized 16ch one, then the plane can go bigger and bigger, brushless powered, nitro powered, gas powered, turbine powered! And you basically have an RC jet costing thousands of $$$, you can see some crash on youtube, it’s scary :-/