I'm hopefully going to Vietnam with my two brothers and sister this summer and i have a question for certain prices since the last time i was there most things were considerable cheaper than in u.s. only answer if you know definitely and have been to Saigon, Vietnam or currently live there

1, what would the price be for teeth whitening?
2, I'm looking for a new drum set, the price should be cheaper there right?
3, Highlights and lowlights?
4, a new guitar amp?
5, slight cosmetic surgery?
6, and lastly for classes of any kind such as dance, language etc.....

I asked about how to say "you" to strangers last time. This time I want to ask about "I". How do I say I to a stranger that is around my age? Do I just say toi? When is toi acceptable.
also how do you prounounce

"a ă â"

i know the first one is pronounced like "ah".
o yeah... is northern accent really different than south. like are a lot of the words different? my family comes from south, but when i listen to northern accent, i can only somewhat understand.