Reach NJP and take a shared cab to Darjeeling. Stay in a guest House or a home stay. Try staying near Chowrasta since then you'd be able to cover all every place by walking. You can also trek to Tiger Hill and camp over there. For food, there are a lot of roadside shops that sell you delicious food at lower rates. You'll easily get meal for one at 30 to 40 rs. When I was there, I binged on a roadside dish called "Faale".
Look for Airbnb and couch surfing. Hire a bike/scooty there for travel. Check the local food joints and avoid fancy bars/restaurants. That should help u
Reach NJP and then Tenzing Norgay Bus Terminus... Take a bus to Darjeeling (110 INR) .... Stay in dormitories near mall road (eg: Diocesan guest house; it cost us 200 INR per day per head on our trip) Take shared cab for sightseeing... There are view points near mall road which can be reached on foot... Darjeeling main (excluding offbeats) can be covered in 3 days within 2000 INR, if planned well We as college students had covered the trip within 1500 INR, since we had special "B Tech" money saving techniques😂 Ping to know more ...