I have a whole mish-mash of extensions, Cornwell, Wright, SO, Craftsman, S-K Wayne, Fleet, and I think even a Proto.
What is my point? Unless you are absolutely obsessed about having them all match, there's no sense in dumping a ton of money into them. You can buy good name brand used ones for next to nothing because people typically end up with so many of them. Locking and wobble extensions may be a bit harder to come by cheap second hand because they usually aren't included as part of socket sets, buti don't think I've ever paid more than a couple of bucks for a used normal extension.