Houghton & Swan 2012:

“If OA were adopted worldwide, the net benefits of Gold OA would exceed those of Green OA.

However, we are not in an OA world…

“At the institutional level, during a transitional period when subscriptions are maintained, the cost of unilaterally adopting Green OA is much lower than the cost of Gold OA ? with Green OA self-archiving costing average institutions sampled around one-fifth the amount that Gold OA might cost, and as little as one-tenth as much for the most research intensive university.

“Hence, we conclude that the most affordable and cost-effective means of moving towards OA is through Green OA, which can be adopted unilaterally at the funder, institutional, sectoral and national levels at relatively little cost.” [emphasis added]

Houghton, John W. & Swan, Alma (2012) Planting the green seeds for a golden harvest: Comments and clarifications on ?Going for Gold?