Spending Round 2013 set out a long-term funding envelope for HS2 Phase 1 (London to Birmingham) of £21.4bn (in 2011 prices). For Phase 2 (Birmingham to Manchester and Leeds) the envelope is £21.2bn (in 2011 prices), with a further £7.5bn (in 2011 prices) for rolling stock. This provides long-term certainty to the project.
In the Development Agreement signed between DfT and HS2 Ltd on the 8th December 2014 (https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/389368/HS2_development_agreement__December_2014_.pdf), HS2 Ltd has been set a Target Price for delivering Phase 1 of £19.34bn, including £3bn for rolling stock.
There is no equivalent Target Price for Phase Two yet.