I'd like to take a monitor with me as a checked baggage, but it is an international flight with one change so it seems quite risky. So I would like to buy one at Colombo Airport duty-free shop. Do they sell monitors there? Would it be cheaper than buying it somewhere in Sri Lanka after arrival?
Also I'd like to buy some HRM watch, either Polar, or Garmin, or FitBit, or smth. Do they sell such things in airport duty-free shops?
The web site for the Colombo airport has a list of shops in the airport. Although I'm a bit puzzled as to how one would buy a washing machine in a duty-free shop, and carry it on the plane, it clearly states that there are multiple duty-free shops selling such home appliances, and TVs. So you may be able to find a monitor (or a TV that would work as a monitor).
Check the same list to see if any stores are likely to sell the other items you're looking for as well.
Whether it's cheaper to buy a monitor (or any other item) in a duty-free shop versus anywhere else is an immensely complicated question which we cannot begin to answer, since it would literally require checking the prices of items in every retail outlet. But you can see this question for some discussion of the relevant topics.
