How to extend your existing Vietnam visa?
Generally, it is relatively easy to extend the visa for your longer stay in Vietnam at present through a travel agency. Renewal for the first time may cost you about 25-30$ (including a handling fee) and takes 03 working days to process (Monday to Friday).
The maximum period you can ask for is 30 days and it costs the same whether you ask for 1 day or 30 days. A second 10-day extension is possible at a cost of around $35-40.
For this second extension you will be asked to show an air ticket dated after the expiry of your visa.