You must be getting sick of me by now
How much of my money could I get back? How quickly could I sell it? If I knew I could sell the bike easily-- and for a decent percentage of what I paid-- I'd feel more comfortable spending more.
Time is your enemy.
If you want to sell your bike, it will really only be practical where they speak English. That means the UK, NL, possibly Belgium and less likely France. Possibly Germany.
If you want to use a local second hand site expect problems without an address. Possible, but more complicated - again language is an issue. Lack of local phone will also be an issue.
Best bet is to bring to a bike shop - and get a nominal price. Sorry.
Of course, if you have local contacts/family who can sell on your behalf, that's different.
Or, if your plans allow it, a decent amount of time in your final destination to give you time to sell the bike. But that's most likely a big city - expensive.
In other words, the more you spend, the less likely you are to get your money back.
It strikes me that there are a lot of variables at play here, and no one has priority.
You want a bike.
You want new.
You want to tour.
You want to sell it back.
You want as much back as possible.
The single most important thing about a bike for a tour is that it is comfortable. If you don't believe me, ask anyone who has tried to tour on an uncomfortable bike!
At the end of a 6-8 week tour what value would you put on being pain free?
If you're in anyway handy, you could pick up a cheap 90's rigid MTB for anything up to €50. Stick on a rack, change tyres, check chain etc. and you're good to go. Have a good look at the wheels. They'll be important. Realistically, you'll have a bike that will get you around for €100 odd. Lots of bike shops in case of repairs that you can't do yourself. You'll pay far more for the bike if you buy through a bike shop. Bring your own saddle!
That's the cheapest way. The more adventurous!
Good luck!