Istanbul to Lisbon

We recommend flying. Try www.skyscanner.com to search for options. It might cost $200, but that's cheaper and much faster than trains. Rick’s Train Travel Time & cost Map gives you an overview of faster train travel times in hours, as well as regular (full-price) 2nd-class fares.

Istanbul to Lisbon by train will be really, really long and there are some tricky border crossings in terms of train travel (eg there are very few international trains between Spain and Portugal and most are overnight-only). I would strongly recommend flying.

Well, unless you would like to spend 2.5 days on buses and trains, I would highly recommend that you fly. Use kayak or skyscanner to find the best/cheapest flights.