Where can i buy nice longjing tea with good price in Hangzhou?

And how do i go there?

It is suggested to go to Jiefang Road Non-Staple Food Market. You can find several nice tea shops there. And the prices are reasonable. The market is located at No.185, Youshengguan Road.

Any idea how to go there?

You can take bus no.3, 34, 66, 105, 106, 114, 151, 276, 290, 591 or 801 to get to 3rd Hospital North Bus Stop. Then walk north around 250 yards.
Or you can also take subway line 1 to get to Ding'an Road Station, Exit A. Then walk northeast around 0.6 mile to find the market.