where are you based ?
i'm a messenger manic so.. sharing my tips:
browsing 'guys' shop sections might be very helpfull.
if you can spend some money, invest in a Martin Margela messenger
if you are based in a Zara enabled area, you might find something there but you may need to check it out regularly, their nice messengers come -thanks god- in limited editions and dissapear very quickly.
if you are lucky you may score a cool bag at Nike, diesel, adidas, the yoga lines or new streetwear labels.
a dj bag could also be an alternative.
they are not 'hot' which makes them 'hot to have'
Printemps (france) has my fave 'affordable' chic messengers for as low as 20 euros euros for a small one, maybe they sell them online
if they have a web-service (worth checking in anycase)
good luck