Typically, my bag is more expensive than my wallet, but I do have another SLG (LV Miniature Lockit in Suhali) that I carry with me that's more expensive than many of my bags.
Hee hee, this question is funny for me because it really depends.
When I'm carrying a larger tote-style work bag, I use an LV SC MM slim clutch in cobalt as my wallet, so sometimes the wallet would be more expensive than my actual handbag (though not if I'm carrying my Birkin)
When I'm carrying a small shoulder hobo, it can go one of two ways - either I will use an older Bally wallet that's nice and small to fit and the bag will probably be more expensive that the wallet OR I could be carrying my Chanel classic double flap and I don't actually carry a wallet at all with that bag: I just slip in my cards and cash and I'm good to go!