You don't need a calculator to work out the prices.
Just check your total order size against the level of order in the chart.
For example, let us say you need to order 15k words. Now, 10k words is $x per 500 words. 20k words is $y per 500 words. However, your order size is less than 20k words. So just check the rate for 10k words which is $3.5 per article of 500 words. So 15k words aka 30 articles is 30 x $3.5 = $105.
It it really couldn't be any simpler. If you want it simpler then you can pay us at a flat rate of $0.01 per word
You just need to match your order size against the chart and get the rate per article. An article is usually defined as 500 words as is the norm. This makes it simpler, not tougher.
And you can always PM me for a quote.
Thank You
Aakshey