I just looked at the eBay auction and was really quite impressed with the Guerciotti shown on auction-the paint scheme and the quality of frame detailing is quite extraordinary and atypical for a Brain tubeset bike . Enuf so that I'd revise my cursory intial estimate to approx. the $450 level on up to maybe as much as $ 525 for such a NOS frameset and in as clean condition as you describe.
I should also expand that while Brain was positioned as a value oriented tube, it's ride qualities are exceptional and it represents an evolutionary step beyond Columbus' earlier top line tubes such as SL/SP, SLX/SPX, TSX, etc.- Brain only lacked in prestige,and gave up only a smidge in weight to the flagship Genius tubing of the time. Tho now discontinued in the Columbus lineup, it is still a useful,viable and desireable tubing for a quality high performance bike.