If you're a buyer, nothing: you'll get a copy of the Home Information Pack free on any property you're interested in. However, a reasonable charge may be made for copying and posting the pack.
With Home Information Packs, the overall costs of buying and selling a home will be similar to the costs before the introduction of the Packs, but will be spread more evenly between buyers and sellers.
The Energy Performance Certificate is a compulsory part of the Pack, and is paid for by the seller.