I think the Visa on Arrival fee remains 1,000 THB until 31 August 2017?

It used to be 1,000 THB, then was raised to 2,000 THB in August, 2016, then lowered (as a sort of tourist promotion) to 1,000 THB through Feb 2017, and then that was extended another 6 months.

That said, I see some reports of Immigration charging 1,200 THB.

A VoA may be able to be extended for a maximum of 7 days; you'd have to apply for an extension at Immigration, the fee is 1,900 THB.

A 30-day Tourist Visa Exemption can be extended for 30 days, with the same fee of 1,900 THB.

It looks like the fee for a single-entry (not sure if that's good for 30 days, or 60 days) Tourist Visa remains 30 euros through August, 2017.