how mutch money do i need to go to Tokyo?

Well as i have calclulated: I have 5000$

900$ - Plane ticket to tokyo and back

500$-1000$ on my hotel/hostel/or some guest house havent figured it out yet :O

250$- Only on train rides (Il be staying and traveling around only TOKYO

100$- a day for food and some crap , il be staying 14-20days

SO is 5000$ Enough??? Did i miss anything ?

If you get your foods at convenience stores three times a day, you can live with $20 a day. Tap water is drinkable here, so you can save some money if you bring a bottle.

Cheap hotels rate are somewhere around $40 per night or even less, so $800 for 20 dyas. You should book your hotel before you leave home to fix the cost.

Hoteiya and Ebisuya in Sanya district are popular among foreign backpackers.

http://hoteiya.blog47.fc2.com/blog-entry-616.html

As far as you stay in Tokyo and use Tokyo Metro for your tansportation, TM is selliong a one day all you can ride ticket for 710 yen (=about $7.50). You can't use it from Narita to Tokyoo since they are not running there though.

Don't get mislead about the metro pass. Yes, it gives you unlimited travel in one day, but you cannot use it for any JR lines or Toei subway. You may find it isn't much of a saving, if any. Use hyperdia.com to calculate costs. If you're flying into Narita, a Suica & NEX one way package would be a good idea. Suica is very convenient and though it doesn't offer discounted travel, you get it at a discounted rate in that package. It can be used on all those lines.

For public trasport in Tolyo JR Yamanote line may be the most convenient. It runs to most places a standard tourist wishes to go.
Single ride in Yamanote costs 130-160 yen, depending on how far you go. Day pass to Yamanote costs 730 yen, so unless you hop from place to place all day, getting a single ticket for each ride you may save a few bucks. I rarely need more than three single rides per day.
Local fast food is very reasonably priced. Check out places where you pay to a machine before entering the place, the machine gives you a ticket that you give to the staff. Usually these places have a large variety of ramen soups, unfortunately i do not know what they are called.
Accomodation is around 3000 yen per night especially in Asakusa. Check Taito Ryokan and K's House. They have dorms or doubles.
Japan, even Tokyo can be done with surprisinly low budget when you know your way around.