Cost of trip

That's like asking how long is a piece of string.

What type of accommodation do you intend to use
How will you travel, by bus, plane or hire a car and driver
Are you a party / night club animal

Give us an idea of the above and someone may be able to help you.

I'll stay in 3 star hotels.  Eat street food.  Maybe a few higher end meal , taxi most of the time, flight from HCM to Hanoi. The tour package   Museums , nit a drinker.  No escorts.. I just want to see the culture. I will stay on a boat in ha long bay.....I'm planing $4000 flight already paid ...

How much do drink?

I don't drink .

It seems you are in HCMC now. So did you meant a 25 days trip to Ha Noi from HCMC?
It depends your spending habit 
Anyway here is my contribution:
Food & drinks    = $180
Accommodation = $ 300
Travel exp.         = $ 200
Others               = $20
                          --------------
Total                  = $ 700

Oh, your budget is not cheap 
If you planned like that it'll more than my calculation 

$4000 is ok

MrshyONE wrote:

I'll stay in 3 star hotels.  Eat street food.  Maybe a few higher end meal , taxi most of the time, flight from HCM to Hanoi. The tour package   Museums , nit a drinker.  No escorts.. I just want to see the culture. I will stay on a boat in ha long bay.....I'm planing $4000 flight already paid ...

You must be rich ) I cant see how you can get to know the culture if you stay at 3 stars hotel, visiting around by taxi, going by tour package and staying on a boat in Ha Long Bay! ) That should be a plan for an elder person which I guess you are not and which should be only around $2,500. Re-plan your trip if you really want to see the culture. I spent 1 month in Hanoi in December last year - stayed at a budget hotel in centre of old quater and the trip costed no more than $1,000. If you go to Halong Bay, should add in a bit.

Plan on $4000 but no need to spend that much. Just good to have some in reserve for unshceduled events.
Take out travel / medical cover too.