Not sure on a graded one, but my Loosie cost me £14 with the 'correct' blaster and an acrylic case.
I would not expect to pay a great deal more than the other variants, its just another common variant to me. With Wally's some see PBP as an enigmatic term IMO and adding those three letters into a description is license to inflate the price, its just a Euro variant to me as there are so many slight variations on this figure.
Unless you mean the light green headed Wally (Meccano) these guys to command a higher price...
http://www.ebay.co.uk/itm/Star-Wars-Vintage-RARE-PBP-MECCANNO-WALRUS-MAN-Lt-Green-Dark-Blue-AFA-Graded-/271494567942?pt=UK_Collectables_SciFi_fantasyCollectables_EH&hash=item3f36565806&nma=true&si=ZTw854GmkTHWRaT0Blx3mgm%252F9sQ%253D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557
Good luck