Hi there,
Please take a look at this; the requested functionality is thoroughly described and explained via this forum discussing the very issue.
https://www.nopcommerce.com/boards/t/16813/fixed-prices-please-instead-of-currency-rates.aspx
Do let me know if you have additional questions or issues we need to clarify.
If you are up for the task, you are very welcome to PM me with a price/estimate.
Thank you in advance.
Best regards
TPS, InHouse