I feed mine frozen bloodworms. He also gets snails that grow in my other tanks. They won't eat pellets or flakes. It has to be frozen or live. I don't think he was expensive. I think he was maybe 7 dollars? He was hard to find though. It took my Petco a couple months to get one in. They're not hard to look after but they do need a lot of plant cover, either real or silk. They're fun and really cute.
This is where I got my info on them when I was researching getting him:
www dwarfpuffers com