Similarly, it's hard to find an inexpensive leather bag that doesn't look cheap. I have a Mulberry messenger that I am very happy with. Got it used off Ebay for 1/3 of the original price. Keep looking at ebay and eventually a good deal will come along. Get a canvas bag for the interim.
Or, for a relatively inexpensive, decent-quality conservative looking bag, check out this option from LL Bean.
I like that bag a lot.