I like the look of those Quiff bags but the price is, as you say, a little steep.
But your friend with the messenger bag has the right idea, except that he needs two, and to attach them as panniers.
Long time ago, when I rode on Dutch vakansiefietse (vacation bikes), Dutch items with every luxury including coat guards in case someone was careless enough to commute on them -- and leave them at the station or in shared parking! -- I saw on the net a fellow who had two messenger bags in leather, same as I had one of, which he'd made quick clips for, which he showed with well-deserved pride, attached to the pannier rails of his commuter, which he rode in a Hugo Boss suit and ankle-length Bugatti overcoat. Not wanting to buy another messenger bag if I didn't like the idea in practice, I bought a couple of plastic briefcases at a poundshop (a dime store) and attached them, and all the weight weenies in lycra suddenly nodded approvingly. It actually worked well enough for me to keep them for a year or so, until it came to me that I don't want to carry a few folders of papers but six bottles of wine each side, and I went over to the open-top Basil open-top pannier baskets I still use, usually only one on offside (the drive side) because it is a convenient place to tie a traffic yellow strap around, which also holds the bottom of the basket to the seat stay, not so elegant but much more convenient.
Still, all these years later, nothing beats the Madeleine cycling doctor's bag for style, utility, space and speed of operation.
