Use the following XPath:
price = tree.xpath("//*[@id='actualPriceValue']/b/span/text()")[0]
The following code checks out:
from lxml import html
import requests
page = requests.get('http://www.amazon.in/gp/product/B00EYCBFDQ/ref=s9_pop_gw_g147_i3?pf_rd_m=A1VBAL9TL5WCBF&pf_rd_s=center-3&pf_rd_r=1YP3T548XBFHJ1RA3EH8&pf_rd_t=101&pf_rd_p=402518447&pf_rd_i=1320006031')
tree = html.fromstring(page.text)
price = tree.xpath("//*[@id='actualPriceValue']/b/span/text()")[0]
print price
Result:
4,094.00
[Finished in 3.0s]
Let us know if this helps.