Alright, I never used Camillo´s Realism mod. I read that he changes prices and durability of vehicles. Is that it? If so, what is the price and upkeep of a Hunter in Camillos?

Man Hours: 80
Cost: 300,000
TU: 150
HP: 150
All armor: 40
Accuracy: 90
Reflexes: 30

I cannot seem to find upkeep.

First I strongly suggest you download free notepad++ to edit xml files, so you wont mess up any file with unclosed tags since it has code highlighting and will color unclosed tags differently, also it shows you the code line.

Then you should make a copy of the whole turtle tank folder in Xenonauts/assets/mods and rename it. Otherwise it might get overwritten whenever I update the mod and your changes would be lost,especially if you have subscribed it. Also make sure your version is higher up in the mod launcher list than the original before you start the game. You can also delete or move the original Turtle Tank folder somewhere else to avoid conflicts.

Okay in your Turtle folder you need to open manufacture.xml and change entries in lines 139 and 140 for man hours and cost.
In vehicles.xml you change entries in lines 126 for TUs and in 127 for HPs. Line 137 changes upkeep,
Sidenote: Giving more then 200 HP will work but will not be displayed correctly in the HP health bar in combat I think. Armor values are in the lines below. Changing Reflexes does not do much I think, having the flame thrower or alenium gun autofire (they are pretty unaccurate) would probably kill your own men even if you tweak accuracy because they do lots of area damage.
However you can play around with accuracy in vehicleweapons.xml for each mounted weapon seperately in lines 87,100,113,126 and reflexes is again in vehicles.xml in line 131.