How can I use feeds tamper to remove currency ($) sign when importing prices?
This is pretty easy.  You can use the "Find replace" tamper under "Text", and then user "$" as the search and "$ " as the replace.  If you want to be fancy you can use the "Find replace REGEX" tamper to make sure you only get the leading $.  IIRC, this needs to include the delimiters.  Using "/^\$/" as the search and "$ " as the replace should work (you need the ^ to anchor to the beginning and then escape the $.  Both of these plugins are part of the base feeds_tamper module.