If you can’t spend much, your best bet is this Tunic. It's a fantastic product, while not very costly. You might also want to consider this Chaps Tunic. It's an item you're bound to love which also doesn't cost too much. You may also want to look at this Caslon Tunic. This item is not expensive either, but it will make a difference in your wardrobe.
If you're looking for something in between pricewise, why not consider this Eileen Fisher Tunic. While the price is very reasonable, this piece is an easy wardrobe update. You might also be interested in this Talbots Tunic. It's an attractive option both price and quality-wise. Take a look at this Black Diamond Tunic too! Great value for your money.