I am not an RAAF collector and know little about these badges, but I can tell you that Wallace Bishop is indeed and Australian jeweler. I believe they began business in Queensland in about 1917 and perhaps are still in business.
I don't think badges by them are all that uncommon. Here is a link to a similar badge by Wallace Bishop that may possibly explain the screws on the back.
www.jkmilitaria.com/Aviation.html
Scroll down to the tenth (second last) Australian item
They certainly made other "sweetheart" and military oriented jewelery as shown by this 1944 advertisement for wedding rings with an RAAF design.......the rest of the page makes pretty interesting reading, too, especially the article about the bloke in the mosquito.
Trove.nla.gov.au/ndp/del/article/42042930
As for price....I suppose its value to you is whatever you paid for it
I Man