Hey, welcome to CT. That is called a cud. It is where part of the die at the edge of the coin breaks off and the metal fills the resulting gap. My guess is $10 or so.
Here is a link, scroll down to 2005 and you should see yours http://cuds-on-coins.com/washington-quarter-cuds-state-terr-2/ I think it is this one, but you have the coin in hand so can better judge CU-25c-2005P-10R(WV)