Riding a bike is part of the Dutch lifestyle and is a easy way to get around. So, it may be a good idea to buy a bike. Dutch people usually do not have fancy bicycles, because if it gets stolen they will not feel too bad.
Most foreign buy a second-hand bicycle. A reasonable one will cost you between 75€ and 175€. You can find them at second hand bicycle shops, at the bicycle parking facilities near railway stations or on https://www.marktplaats.nl/.
When you buy a bicycle make sure that its lights work and it has a sturdy lock. Even better is to buy a chain and padlock so you can fasten your bicycle to something when you park it.
Traffic rules for cyclists: As a cyclist, you too must obey the traffic signs and rules, and stay in the bicycle lanes marked on the street. As a rule, cars that are turning across your path are supposed to stop for you, but it is wise to watch out. You should also signal with your arm if you are planning to turn. You can be fined for riding at night without lights and for using your mobile phone while on the bike.