What will be the total duration and cost of Annapurna Base Camp trek?

Duration

Is it feasible in six days? Certainly. Is if feasible for you in six days? That depends on you.

In general the organised treks will take a few days longer than what you propose. But those are meant to be accessible for overweight, middle aged, European coach potatoes. If you are in reasonable physical shape, six days is fine. If you are really fit and sporty you could even go for four days (or even less). But why hurry? From your description it sounds like six days will be a good option for you.

For such an elevation AMS is rather rare. You would have to be unlucky to get it. But if you develop symptoms you should turn back and descend. You stated so much yourself, but I like to reiterate it because we are talking about a potentially life-threatening situation. Being short of breath in the higher parts is no problem and is even a given.

Cost

I think your estimate is possible if you live frugally, but will be close to the limit for two meals + night. The cost is usually in the food, rather than the nights.

I came across a blogpost that gives a nice overview on prices on the Annapurna Circuit (not the Sanctuary trek but it is similar there) in the different villages in 2015. Scroll down towards the end just above the title "How to get there" on that page.

You will see that with two meals a day you get quickly to your scheduled budget and even will pass it on the higher parts. Personally, I would rather budget 1500NPR/day and be happy that I manage to stay below budget than having to worry every meal about the total cost.

In the Khumbu I once entered a place that had on the outside a small sign saying "Nepali Hotel". It turned out to be a place where guides and porters were staying. It was very basic with everybody sleeping in one big bunk and as a meal the choice between dal-bhat, only dal or only bhat. So no choice at all. Needless to say the cost was a fraction of what I paid in a real lodge. I assume that similar accommodation exists in the Annapurna region. But for a white Caucasian, obviously tourist, it is hard to find. You, as a Nepali, might have more luck. Socializing with guides and porters might save you some money in this way. Those guys know the valley, have been there a zillion times and might send you to places where they would not send a Western tourist.

Other costs you might be forgetting:

• Transportation to Nayapul: wikitravel states 110-200NPR for the bus Pokhara-Nayapul. For both ways count on a total transportation cost of 400NPR.
• Trekking permit: the NTNC website states a fee of 200NPR for SAARC citizens. I could not find any exception for Nepali citizens, so that appears to be the fee that will apply to you.