What kind of spam are you interested in my friend? Mail, social networks, messengers, sms? In any case, it is unlikely that you will be able to do without costs. But you can minimize your costs after you acquire the necessary tools and knowledge. At a minimum, you can start with mobile spam using sms packages and a gsm hub with physical sim cards or by purchasing an inexpensive WhatsApp or Viber sender soft. But if you are not going to do it for a very long time and a lot, it is always better to pay for the work of a specialist.