Walekum Salam, Congratulations buddy on getting married
With this little budget at hand, I highly doubt if you can have a comfortable trip to Gilgit Baltistan. Due to long distant routes in GB, the major chunk of expense will be on transportation. I would suggest you to plan a relaxing trip to Galiyat side, explore Islamabad, nathia gali,you may extend further to Mansehra, Kiwai , Shogran, Siri Paye etc.
For a budget constraint trip, my advise would be.
Take a economy class train journey.
Book hotels before hand, through websites like Booking.com or Airbnb
Rent a car before leaving which should pick you from Railway Station and tell them all the places you want to visit. This will give you overall idea about transportation expense. (Take rates from couple of rent a dealer to make sure you get the best rates)
But still if you want to explore Gilgit Baltistan, you will have to travel through public transport considering limited budget. Best would be NATCO from Rawalpindi to Gilgit (Approx 18+ hours journey). Refer link below for NATCO Rates, Schedule & Routes.
https://www.natco.gov.pk/NatcoWeb/Routes/Natco-Express-Schedules-Fares-Routes
From Gilgit, you may visit Naltar Valley, Hunza, Attabad Lake, Minapin, Passo Cones, Khunjerab Pass etc.