Looked at the BrownDog site and they are fine with 2134 pricing.
The adaptor? Solder in, from the look of it, so I don't know what that buys you. Plug in would be fine for swapping opamps. I guess I'm not current on what people are doing. I guess I don't know what the advantage is of soldering in an adaptor in which the part has to also be soldered in. The CMOY I built has a plug-in header so if I ever get the urge, I can swap opamps in seconds.
The single to dual adaptor makes sense.