"Thailand and Malaysia are free whilst Vietnam is 55$ and Cambodia is 20$US
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Thailand is free for many western countries, if you stay 30 days or less. Some countries do have to pay for a Thai visa.
The VN visa is actually $25. But, the price varies from country to country. I have bought VN visas in Phnom Penh for $28, figure $30 now. This is using a travel agent or business. It is not worth your time/trouble to save $5 by doing it yourself IMO. I was charged $45 for a VN visa in the US, $55 in Singapore.
Another option if you are flying into VN is the 'visa on arrival' system. $25 stamp fee, $17 for the approval letter. I wrote about this in my blog, under 'Off to SaiGon'. Good luck.