Running

Yeah, go to the track, it's worth it especially if you're going to run long term. But what's even better is stuff like soccer fields, just don't wear cleats because then you're damaging their grounds. Depending on where you live it may be hard to get ground better than a track.

"Camelbacks" are incredibly cheap these days. You can buy cheap ones on Amazon/Temu or even military surplus ones. But it's worth getting one with small pockets to hold phone/keys/wallet while you run. Don't feel like you need to buy ultra light shit either. If you train in heavy/cheap equipment, it's easy when you run the marathon. They'll have water stations out and everything, you don't need to carry anything.

But especially if you want to try occasional trail running to break up the monotony of regular track practice, you'll want to have your stuff with you.

A sprained ankle on a track sucks.

A sprained ankle 2 miles away from your car in a state park has literally killed people before. Be very aware about when what you're doing crosses from running to hiking and don't be afraid to bring a lot of gear even just for the weight for training.

The only thing that's worth spending money on is shoes, and you should prioritize safety/support and ergonomics over "racing" shoes.

You can race in training shoes, you can't train in racing shoes. They won't hold up to it and neither will you.

Everything else about running can be cheap.