How much does it cost to add a glider rating to a PPL?
If you're in Romania, are a Romanian citizen and are under 23 you can do it for free in the Romanian Airclub.

Otherwise it's 15 eur/winch launch and  25 eur/tow at around 300m.
I'm not sure if there's any deduction from the glider training if you have ppl but I know that if you have the glider licence you get a shorter training plan for motorized aircraft.