It's not only the minimum temperature, it's also how high the temperature gets during the day. If they got 1C as the absolute minimum for a couple of months but with the maximums getting around or over 30C then there'd be no trouble. In fact they'd probably flower better. If the temperatures didn't go up much during the days there'd be no trees. You need to look at the 'whole picture'.

minimum nocturne in the afternoon the temperature up (in greenhouse)

so at 35 degrees farenheit (nocturnal) survive for two or three months?

Should- that's above frost. Mine see that every year,Once or twice we touch 0C. But that's a 6 year old plant in ground,and the below 35f is only a few nights a year- not two months worth. Young plants get hit with a 0C and they are either killed,or killed to a stump..and that's just like starting all over.

I would say we average for the 2 months of Dec-Jan about 15C as a high and 6C for an average low. So,thats quite cool for a tropical. So, a greenhouse in that range in colder climates should do the job.

because i would like to keep the greenhouse heated to +2 degrees centigrade if i hold it to +6 or +10 it costs too much for two months

The my greenhouse is in polycarbonate of 16 mm dimensions 9 feet x 16 feet ,9 feet height,when the external temperature is 12 C degrees, in the greenhouse is 14 C degrees ..I don't know when will there be frost wich will be the difference between inside and out?depending of the year...the last year was all days low 0 C,(in the night),other years some days (3-4 days low 0 C) in the every year,but if the temperatures are what last year i'm not disponibile to expense very money to heat at +6 C or +10 C degrees

You ever consider a smaller GH enclosure in the greenhouse? Putting a heat mat under the Mango?

Do you have an example, a link or scheme,? I don't know this method..in my greenhouse I have now very plants of citrus,and other exotic plants :

carica pentagona,guava,passiflora and musa plants..I have a biogreen palma heating 2kw connect with thermostat ..the problem is to keep the survival of plants and to spend little money..is first time that I have a heating..last year I not had the mango..I have buy for my first time this years the plant of mango and other exotic plants last year I had the citrus and not I had the heating..I think now at what will be the costs for heating I would like test the costs..in italy the cost of elettricity is 0,46 euros (2 kw) every hours..(and the days frost with minimum 10 hours for every days) 0,46x10 = 4,6 euros for every days of frost (last year 2016/2017 60 days of continuos frost in the nights)

so if it was not mango and other exotic I could keep lower temperatures

Well,Mango is much more tender then Citrus. I'm thinking you could make a small greenhouse to set on the larger greenhouse's bench. Putting heat under that one plant should not be expensive. Plus,on the bench keeps it from cold lower air.

But,Mangoes do make good potted fruiting tree's eventually.

The min must be above 0°C, and max above 10°C.....in the greenhouse (if there is sun) it's not a big problem for the Max, but for Min you must think something for the coldest nights.

Also- min is always subjective. HOW LONG,at the minimum is the problem. A few minutes? Or all day?. Why it is best to keep anything below 35f or 2C or so all the time as coldest temp. If you are in a climate that stays at even 2c all day and night and more..THAT might kill them too.

Yes, for Mango the time might be more important than temperature..