Actually, coming from the west it's amazing how inexpensive India can be. Of course on the parikrama everything's included (except drinking water, snacks, and sundries). It is customary to make a small donation at each temple we visit (there are quite a few). There is no fixed amount for this, it depends on your means and generosity.
If you are flying in to New Delhi, your largest expense will probably be travel to Kolkatta, then on to Navadvipa. You will need to change enough to cover the trains, hotel, and taxis. The Navadvipa Parikrama festival fee is around US $50 or equivalent in Euros or Rupees. You're looking Rs 250 (or so) for the taxi to Paharganj plus Rs 300 - 400 (approximately) for the hotel plus incidentals like meals and bottled water.
Note: In the past I was told that this section is misleading. She said that sometimes devotees come and spend all their money buying things and end up borrowing money from other devotees before the parikrama is over. So, if you think you want to stock up on kurtas, dhoties, saries, incense, and gifts for the whole family, then be sure to bring extra cash. OK?