Buying puppets that are already made is more expensive than making them yourself but, obviously, the trade off is the time it takes to make them and the skills required to make them. Buying one starts at about $75 and goes to $200 or more for really nice puppets. We use a combination of both. Puppet Productions (http://www.puppetproductions.com) and One Way Street (http://www.onewaystreet.com/) are the primary providers of ready made puppets. You will also find other individual sites similar to mine that sell completed puppets. They also sell pre-recorded scripts. There are patterns for making puppets (in fact I still have a few left over from when I used to sell them). You can get what you need for the eyes and mouth at most hobby stores. The fabric is a little harder to come by. I think One Way Street sells some but it's probably expensive. You can go to my Links page and get some ideas of some of the places that I have seen good puppetry stuff.
Here are other sites where you can purchase puppets:
http://folkmanis.com/ They have great animal puppets but I wouldn't buy their people puppets. Only wholesalers can buy them here but other sites sell them to individuals.
http://www.americandreams.com/puppets/ This site sells Folkmanis Puppets. This is where we buy them.