Payment gateway providers and other payment providers rarely have fixed pricing structures but they may have pricing brackets or guidelines based on your turnover and/or number of transactions per month. Most charge an annual fee and either a monthly fee and/or per-transaction cost. Some include a certain number of transactions for free each month. Some charge setup fees, others don’t. It’s a bit like choosing a mobile phone plan, and your best bet is to shop around to find the pricing structure that best suits your business size and stage of growth.