It depends, in large part, on market conditions. It also depends on the motivation of the seller. Realistically, in most cases, I'd say look at everything below $225,000. Don't set a bottom limit on it. If you set it at, say, $170,000, you might miss a really great deal at $155,000.
So at least start off and see what's available at maybe $225,000 and below that meets your criteria--location, number of bedrooms, number of baths, age, style, etc. Then take a look at what $225,000 (list) will buy you. Then take a look at what maybe $200,000 will buy you, and $180,000, and $160,000. That'll help you narrow down the price range.
Realistically, not too many homes listed at $225,000 will come down to $180,000. But some will. And you may find something at, say, $219,000 that can be negotiated down to $189,000 that you'd be happy with.
So--start out fairly broadly. Then narrow it down.
Your Realtor can give you more information and more strategies.
Hope that helps.