Purchasing green power and carbon offsets on five-year contract, as required under LEED v4, will represent an added cost.

However, projects are often surprised at how affordable renewable energy credits (RECs) and carbon offsets can be. The cost represents an investment in a project somewhere
else that may not have been viable without the market demand, and such off-site projects are often more cost-effective than achieving equivalent reductions onsite.

That being said, reducing energy use by the project is an immediate way to reduce both the cost of this credit, and a way to earn other LEED credits while also reducing long-term operating costs. 

Pricing for carbon offsets is market-based and may fluctuate; check with suppliers for exact pricing. Carbon is a global market; pricing may rise if you choose to focus on local or regional projects that generate offsets.

Cost Synergies

EAp2/c2: Energy Performance