Free SIM Cards
You often need to give a mobile phone number in applications. Like with email addresses, these can be abused, so the obvious solution is to have one or more mobile numbers that you can use without giving your private numbers.
If you do not wish to use Credit or Debit cards online, you can still make safe purchases by using a prepaid card or voucher. This essentially works in the same way as a credit card for the purposes of making a purchase, but the risk is limited to how much cash is actually preloaded.
PayPal is almost essential, considering the hold that it has on financial transactions, especially small private transactions. Sign-up is free and charges only get taken when a transaction occurs. To accept credit/debit card payments regularly, you will need a premium or business account.
Web Site Hosting
If you want to run your own website then it needs to be hosted somewhere. There is free hosting available on some of the links below and sometimes these offer free domain registration too. However, if you do want a commercial website, you will need a more comprehensive service and then you will need to pay. This does not need to be particularly expensive, though, at least not in terms of money. The most expensive element of running a website is the time that you have to put into it. Building and maintaining a website is not easy, even with tools to help you.