I am currently staying in Thailand on a 90 day, non-immigrant ED VISA, single entry. I would like to travel to Vietnam and Bali. How can I arrange more entries on my current VISA?

You could get a re-entry permit that would keep your current 90 day permit to stay valid when you re-enter the country. It would give you no extra days.

As single re-entry permit costs 1000 baht and a multiple 3800 baht.

You must secure a re-entry permit from immigration. 1000Bht single entry.

Note the re-entry permit only preserves your current "permission to stay" date.

How do I obtain re-entry permit from immigration? A trouble is that I only speak English, so telling a Thai person at immigration may be difficult...

Most people that go to an immigration office do not speak Thai.

Complete a TM8 form with an attached 4cm X 6cm photo. Download: http://www.immigration.go.th/nov2004/download/pdf/tm8.pdf

You will need a copy of your passport photo page, visa, entry/permitted to stay stamp and TM6 departure card.

How do I obtain re-entry permit from immigration? A trouble is that I only speak English, so telling a Thai person at immigration may be difficult...

SURPRISE !

Many Thai Immigration Officers speak and read English !

You will be understood.

As far as I know a 90 days ED Visa is single entry only.