I have 3 Painted guitars signed by Bluefest Artists how much should I sell them for being for charity ?

I have 3 handpainted guitars by myself with Indigenous Artwork and have had them signed by Artists at The Byron Bay Bluesfest such as Ben Harper , Jack Johnson , Xavier Rudd , John Butler , Missy Higgins , Kasey Chambers , Jason Mraz , The Veronicas , The Waifs , The Cat Empire , Tim Finn , Taj Mahal , Mavis Staples , CW Stoneking , Seasick Steve and many more .... These Guitars are to be Auction peices to raise money for a Tibetan Refugee Centre in Northern India . It is hard to estimate a good price for these unique guitars . I thought maybe by posting a question here I could get an idea ... To see the Guitars before answering checkout Tibet Guitar Project on FB.