I've been absent from the hobby for awhile, but I'm slowly getting back in. I don't know much about the GSO area, but a friend got my 5# tank refilled somewhere there near his work (in GSO) for much cheaper than that. I'll ask him and let you know.
I don't know about pet shops.
$62 sounds like a good deal on a 5# tank. I haven't bought one in years though. I think mine was more than that in 1996. You wouldn't need a larger one. Mine lasts months on my 75gallon.
I wouldn't get the regulator from the welding store. They don't reduce the pressure enough and you still have to get a needle valve. I have 3 of THESE
. I love them. They are regulator, needle valve, solenoid, and bubble counter all in one. You might even be able to find a better deal than this. There is also a model by Milwaukee that many people have and love, but I have no experience with those.