Believe it or not, stamp collecting could be fun and cheap. What you need to do is to ask your friends, family members, working colleagues, penpals or even strangers for stamps from their letter correspondances. I bet some of these people would not mind sparing you the used stamps (otherwise some of these letters/covers would be finding their way in bins). Well, I was a bit lucky back to 1995-1998 when I pursued my study in the UK, and I met many international students there. These peer pals were more than happy to help me in my stamp collecting. I got many stamps from "difficult/rare" countries such as Eriteria, Ethiopia, Uganda, Tanzania, Niger, Senegal, Tunisia, Morocco, Jordan, Kuwait, Oman, Malawi, Republic of Guinea, Ghana, Cameroon, Sudan, Togo, Mali, Ivory Coast, Burkina Faso, Bhutan, Cambodia, Colombia and many others. I was totally overwhelmed by the responses that I got from these people......... some of them even went further by asking their friends for stamps on my behalf!
These stamps are postally used stamps, and they have fulfilled the requirement for being a stamp by subjecting themselves as the postage payment on the letters they carried. They are different from CTO (Cancelled To Order) stamps. I don't fancy CTO stamps. I like nice clear postally cancelled (from letters) stamps, and this type of used stamps is particularly uncommon and more valuable.