Janakpuri, rajouri and patel ngr are all costly for renting a flat.
If he's a student, he can get a 1bhk(or PG) at cheaper rate in tilak nagar or subhash nagar. The area lies between the way from Janakpuri to rajouri along the metro line. Its connected well with metro.
One can easily get good and cheap accommodation in this area as there are many private colleges nearby. Also, its near the Tilak ngr main market, so getting groceries,clothes, books (yes, there's a dedicated book market in Tilak ngr) etc. will be easy.
btw,
There is a pg/hostel near my house, but its quite far (around 10 mins walking from Janakpuri East metro) or ~2 km from Janakpuri West metro(via metro feeder). Its located on the Outer-ring road near Vikas Puri crossing. So, bus-stop is adjacent to it. Private Metro feeder service is frequent(1 bus every 2-3 mins), and Janakpuri West metro station is just 2 kms away. Environment is good,students living over there seems nice and security is good (due to seperate girls hostel few house away :bleh
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Don't know about the food quality though. Found many students enjoying "Tikki" and "Gol gappas" at the Tikkiwala sitting near the hostel.
One can either opt for such accommodations which are easily available in Tilak ngr and Janakpuri (dont know about rajouri, accommodation in quite costly over there) or rent a flat and live on its own.