First of all, just assume/calculate your hourly rate. Normally, if you are an specialist, you have 2,496 working hours in a year.
Just calculate your or your concerned staff's total expenses in a year including visa fees, rent, food, transportation, communication, salaries, air-tickets etc.
Divide these "annual" expenses by 2,496 and you will get hourly expenses. Multiply this actual hourly rate with 1.5, considering a fair profit of 50% of cost incurred.

Now, calculate the hours spent while preparing the renderings and multiply it with your hourly rate, add expenses for Stationery e.g. Printouts, CDs etc.

You can charge your Client with this amount. You may even add a little more amount for bargaining purpose as the Client may ask for a discount.

If you are a part-timer, you can offer a good discount to your Client.. it's upto you !!

All d best !!