Some other thoughts, written in 2nd person like somebody else asked
If you really want that job...
...perhaps because it's that fantastic Fortune 500 or cutting edge startup that works with Star Trek-like technology... you have to lower your expectation. After all, it's market's offer&demand law
Don't undersell yourself...
If you correctly computed that 100 is the minimum wage to get a decent life, don't go below it at any cost. Maybe for 90 or 80 you will still be able to pay your rent and bills, but what is it for? Why giving up what you already have? Be firm in declining any offer below lower bound.
This assuming that the number of 100 is statistically correct.
And don't even try to oversell...
Try to be modest, and if that Glassdoor salary is considered average, try to count that as upper bound. Try to understand the level of meritocracy in that company. Of course the meritocracy scenario is a best-case. Evaluate carefully what kind of environment are you going to join.
But anyway, in general, if you end up asking for too much on first chance, you have a high percentage risk that there will be no negotiation later, as stated in the question.
Remember the costs
Relocating costs. A lot of money. Your family may help. Sometimes you will need to borrow money from a bank. Take this into account. In face-to-face, try to explain, and try to be very modest, that you will be needing extra resources and that need justifies your demand. Don't act like an IT rockstar, it won't work. Work hard and become a rockstar day by day.
But be a little like a rockstar
Since they called you on first hand, and since you said that your current salary is above the average, remember that and try to use it in face-to-face negotiation. That may be an argument. Since you cannot compare the absolute value of the current vs their salary, use proportions. Try to negotiate as being paid "X% above the average" is an equality condition to your current status. Everyone want to improve their status.
- Recruiter (doesn't know your salary yet): "Don't you believe that your current expectation of 140 may be a little excessive?"
- Candidate: "Well, let me explain. My current salary of 50 is 20% higher than the average salary of 40 [better citing official statistics or articles]. I have taken a look at some statistics about your city. I think that the mean salary for that position is 100, but I also expect that your tax regime is significantly higher than mine".
Of course one has to find much better words than those. And again, especially when facing professional recruiters, don't act like a rockstar (don't overestimate yourself, be modest).
Eventually such kind of approach may not necessarily end up in being discarded by the company, especially if you ask your demands without leaving all doors closed. Close only the door below 100 and don't let them find, otherwise they will stick any offer to 100. See last argument in that case.
That company may be hiring in a place thousands of km away for two reasons: 1) they are desperately looking rockstar ITs, so you won't be getting that money unless you really rock more than other candidates (but if you do, here's your rich payckeck), or 2) they are under spending review and need some cheaper workforce. Get more and more information about that company, and if you ever find that the 2nd is true, try to be happy and wait for the next chance, if any will be.
It's not all about money
Kudos to @EdHeal for this. Never ever end up underselling yourself, but remember that the economics is just part of a job retribution. If the environment is good and pleasing, if that company is already (or is promising to) changing our world, you might be wishing to be part of that change. That has a value. A value that cannot be scaled with numbers. But that may negatively affect your compensation.
And don't be over-optimistic.
Dreaming is beautiful, but we must wake up eventually! Accept that they will offer less than expected, evaluate, think, and be ready to say no. "The train stops only once in your life" a proverb says