If you're on a thrifty budget, your best bet is this Theory Crossbody. It's a great product, while not very costly. Another strong contender for your wardrobe is this Theory Bag. While the price of this piece is not too high, it will certainly attract a lot of attention.
If you're looking for something in between pricewise, look no further than this Theory Tote Bag. This item doesn't cost a fortune, but definitely deserves a place in your wardrobe. It is also worth looking at this Theory Crossbody. It's an attractive option both price and quality-wise.