Hey Rahul, You can visit following places in Ahmedabad where you can enjoy with your friend : 1)Jamma masjid 2)ISKCON temple 3)Sabramati Ashram 4)Bhadra fort 5)Sanskar kendra 6)Rani no Hajiro 7)Nagina wadi And for budget stay you may search for Zostels or hostels on google (www.hostelworld.com).
I suggest you go to Adalaj ni Vav. It has beautiful architecture.
You can also go to Akshardham temple in Gandhinagar, light show happens every evening over there.
There are many cafes and lounges in Ahmedabad. You can try Cafe Mocha or Cafe Baraco at SG highway.