Thought of you and this thread again today as I was browsing through the dog.com catalog.
They have a bunch of pretty stylish bags around $30 and under! They aren't super inconspicuous (they do have the non-hidden mesh on the sides) but if you aren't particularly looking for that I thought some were quite cute (and affordable!)
I am particularly in love with this one:
International Pup Carrier - Dog.com