There is a lot of things to take in to account other than just the main price , I asked your question couple months back and after some research I got myself some answers that might be useful for you .
-When you make the math do not just add the lowers cards prices , You should always add the others costs that you will pay running this lowers cards ( risers , etc )
so while you thing 1050 ti will cost you only x in reality it will cost you x+y . so for example if 1050 ti costing you 145 you should add 10 for the riser which will become 155 . remember we only adding riser price because with 1080 ti you will only run one card no riser ! . also with one card 1080 ti you probably can get any cheap used motherboard that will do the job for you , While with 3 cards you need to find motherboard that can carry 3 cards ( it is very easy to find I am just saying
)
-There is very important factor people need to look at before buying ( most of people I meet do not even think about it ) How easy and how much I will be able to sell my card in the future even if it was for upgrade or for giving up on mining ! ( 1050 ti will probably be an outdated by then )
-Other very important thing is the space , Are you planning to increase your farm in future or you are going to stop at this !
now answer all this questions and the answer will be clear , There is no one answer in mining every one have different needs and different plan , You first need to put a plan .
Now with all that said I have to say I have 1050 ti and it is really good mining card I get with it 15.5 with power at 80% and boosting rams too 1000 without hanging or anything . Someone told me it is because all the ram in 1050 ti cards is samsung ( I am not sure of this tho )