I am a frequent traveler of isb-lhr and vice versa i have to travel around 4-5 times in a month. My car consumes around full tank of fuel i.e 50L for isb to lhr and return back. if we calculate fuel costs 65x50=3250 and toll tax 510x2=1020 total is around 4300 and time consumed for single side is around 4hr.
once i traveled with PIA and fare was around 6k and reached in 40 mins. 3300 is bit high considering other bus service providers, 2-2.5k would be more sensible.