custom module needed

Seed Sharing Module
Type of site:
Non-profit community site. A state-wide gardening club.
Required by:
November 1, 2011.
Budget:
??? willing to negotiate fee.

Process that this module will enable online:
In the fall, members donate to the club batches of seeds from their gardens, accompanied by a list of them. The seeds are sorted and packed in small allotments. In January, the list of all available donated seeds (includes donor name) is published and members place an order for seeds they would like to get (up to 60 choices). The orders are filled on a first come, first served basis, and some substitutions are made for seeds that are out of stock, at the packer's discretion.

Description of functionality:
1.The only input is the name (eg. Paeonia peregrina).
2.One page user interface for members to simply type the names of seeds they wish to donate in a list. I think each entry in the list needs to be/become a separate node so that they can be later assembled in a seed order.
3.Ability to create a list of any length; some will be quite long (~100).
4.Ability to associate user with each donated seed. Do not merge similar seeds from different donors. (eg. Paeonia peregrina - John Smith, Paeonia peregrina - Jane Doe)
5.Ability to add items to database in multiple sessions. No need to associate input from different sessions.
6.Ability to prevent duplicate input (i.e. adding Paeonia peregrina more than once by same user not allowed, or duplicate entries not processed.)
7.Ability to collect names of seeds to assemble an order in one session up to a maximum of 60 selections. List of available seeds will be thousands of entries in length.

Any combination of existing modules plus a custom module is welcome, as long as there is a solution. The key to this solution is the ability to easily list seeds to be donated by a member. Assembling a seed order is not so critical.