There is a saying in Arabic my dad used to like: The expensive is cheap! In other words, you get what you pay for. Of course this is not always true, but if the so called expensive item or service is of top quality then it is true.
What you must realise is that a significant and quality hair transplant can take a whole day and involve a large team of highly trained professionals. That is what produces the results you see. In the countries you mentioned there are regulations, standards and accountability. Most of the doctors you found expensive also invest heavily in travelling and taking time out of their practice to continually educate themselves and their staff in the latest techniques and ideas.
Cheap surgery is exactly that. Either the staff and the doctor are not getting paid enough, or they have to cut corners so they can do more 'cheap' surgery on that day. Do you want to be treated under those circumstances?
Finally, if cheap surgery results in a complication or an unnatural result, you will regret it for a very long time if not the rest of your life and of course it will cost you a lot more money!