I looked up the cost of transport for you. Tel Aviv to Akko by train (one way) is 65.50.
Jerusalem to Ein Gedi by bus (one way) is 32.50.
But the good news is that Jerusalem to Tel Aviv by bus (one way) is only 18!
What about things like admission costs? For example, the Israel Museum is 32. The Ein Gedi national park is 23.
Entertainment? Obviously the cost of that depends on what you want to do.
It sounds like you are planning to buy shekels in your home country before you arrive. It's always cheaper to buy currency in its own country. Unless you have a stash of shekels already, wait till you get here. There are exchange bureaus all over the place.
I did a very rough calculation as follows:
Accommodation 100 a night - this is not unrealistic; I think 50 is very unrealistic unless you go to one of those rock-bottom places that Ros85 mentions.
Fares 80 a day (obviously you won't travel every day, so this is perhaps a bit on the high side, but not much)
Food 50 a day, very stingy
Museums 20 a day (averaged out, some days you won't).
Multiply by 6 and that comes to exactly 1500. Nothing there for any other contingencies. You don't want to have to worry about whether you can afford to buy a glass of juice or hop on a local bus to save a long walk. I think you need more.
You say "in a week" - do you mean you are travelling a week from today? Bear in mind that it will be Easter, not a holiday in Israel but a very busy time for tourists and pilgrims. If you don't have accommodation booked you might find yourself having to pay a whole lot more.