What is a reasonable Attorney Fee?

 In Webster Dictionary, "Reasonable" is defined as "according to the rules of logic". As law states, in collection process for property tax liens reasonable attorney fees can be charged and the upper limit for those fees are stated depending on the face value of the tax lien. But in legal logic, what is reasonable? 
        Some attorney might say, his standard fee is 2000$ per hour and charge his clients accordingly. And client has the option to choose that lawyer for whatever task they have at hand. In a free market, market decides the fee. Unfortunately, in property tax liens, the payor of the attorney fees actually do not have any control over the fees which is why we need the existing state laws.
      But what is not reasonable is easier to define. For example, an attorney cannot charge a different rate for same amount/kind of work depending on a client. Such an action will be discrimination and Respective Bar associations discourage their members from such practices. By this logic you cannot change a different attorney fees for similar property tax liens purchased at the same time and are at the same stage of collections. It does not take more work to collect a $300 tax lien versus a $700 tax lien. Such practice should be reported to the Bar Association as a discriminatory practice.