2 single entry visa's instead of multiple entry

Hi,

I'm flying to Vietnam on august 15.
After travelling 3 weeks in Vietnam, I'll fly to Taiwan for a holiday of 2 weeks. After these 2 weeks, I have to return to Vietnam for one day because my return flight to Holland leaves from Ho Chi Minh.

My question:
Can I use a single entry one month visa, leave to Taiwan and return within two weeks on a new single entry one month visa?

As two of these visa are cheaper than one multiple entry 3 month visa.

Thank you very much for your quick response!

Marlijn Hoefnagel