There are actually multiple ways of creating a wordpress site. One would be the already available template route where in you add the template, configure it and simply add content. If that is the case the number of hours involved are less and thus the costing is reduced drastically.
But most clients need a custom design. They provide a design based on which you need to develop a template. So if there is custom coding involved, it would definitely take up a lot of time. It would involve hours of work to get the template output as per the design provided. This increases the cost.
Now a days clients also choose to take the middle path. Find a template similar to what they have in mind and have the template customized. This is a lot cheaper than getting a custom template made and yet gives their business a unique look.
Given all that I could hardly guess any one providing any of the above solutions for less than USD 300. I think any developer given the time one needs to put in to such work would need some basic amount from each work one does. So given the links you have provided look like custom works such work would involve hours of work and hence higher the costing!