Our national organization has a valuation guide you can use as a guideline. You can find it here: http://www.goodwill.org/wp-content/uploads/2010/12/Donation_Valuation_Guide.pdf
Usually they give you a donation slip and you calculate it yourself and file it at tax time. They do this at Salvation Army. Call Good Will see what their process is. Good luck. God Bless
Thanks! Your answer is awaiting moderation.