1988 CR250R full rebuild?

I have an awesome '88 CR that needs a full rebuild of the engine. When I got the bike, it ran ok, then the frikin top end blew up. The piston intake skirt shattered. I took perfect care of the bike and everything. The funny thing is, when I took the jug off, the original stock piston was still in there. The bike never had a top end rebuild done, amazing it survived 20 years with out one. Anyway, I would like some information about what you guys think it would cost to get a entire rebuild of the engine, top and bottom, to get this beast back from the dead. Thanks.