Make An Offer
This extension adds a Make An Offer button to the product page of Spree. It accepts an offer price and an expiration date. On submission, an email is sent to the site order email. The extension also adds an Admin feature allowing the site administrator to accept or reject the offer. If accepted, the product is added to the user's cart at the offer price. Check out then happens normally.
Install Spree (Requires 0.6.0 or greater).
Put this gem in your gemfile
gem 'spree_make_an_offer', :git => 'git://github.com/pzupan/spree-make-an_offer.git'
Move assets from gem public into your app's public directory
Currently this gem adds the Make An Offer button to every product. The intent is to create a default of all products or the ability to select specific products which will accept an offer.