A sturdy, used, road-oriented bicycle. $200 won't get anything too fancy, but cycling is a low-impact activity that -- given the right places to bike -- is meditative, improves cardio, facilitates independent exploration, and also happens to double as transportation.

I specifically say "road oriented" because I don't want to necessarily endorse all road bikes, like the ones with carbon fibre or "Tour de France" pedigree. Likewise, mountain bikes with full-suspension sap energy away from the steady cadence ideal for a good workout, in addition to generally costing more or delivering less-than-stellar performance at low price points.