I have 20 green-banded gobies in a high-flow 150g tank. They are doing great. There is a vendor on an online auction website (it'll be your first guess) who sells 5 for $15. Check the website every month or so.
I can generally see about 3-4 of the gobies at any given time, which is why I got so many of them. They get along well with "personatus" gobies and lots of other tiny fish I keep in the tank. (Including blue-stripe pipefishe, yellow-lined clingfish, sailfin blennies, pygmy wrasses, etc.)