How much does replacing an engine of the 2011 chevy express 3500 cost

I'd get another opinion and even see if you have recourse against the vehicle seller; sounds like you maybe were put in a very difficult position. If you need a quote on replacing an engine, check with any local "RepairPal Certified Shop" near you using the links th on this page to search. This kind of estimate requires "real world" attention and addressing, not an average or range of pricing.