A decent bike needn’t be expensive. For as little as 300€, you can have a new bike that’ll do just fine for recreational use and simple commutes. Used bikes can usually be had really cheap, too, but for that you’d best know how to check the components and what to look for.
Race bikes, mountain bikes and pedelecs are a different thing, but those are either specialty sports equipment or luxury items.
Either way, (normal) bikes are easy and cheap to maintain, if used correctly.