Board members are your best champions and should be leading the way for the rest of the community as to why it is important to give to your organization. The size of the gift is not always as relevant as your board members understanding that financially supporting your organization is a part of their role as a board member.
Board members are sometimes given the option of either personally giving money or finding sponsorships/donations up to a certain amount. One common practice in small/medium size organizations is to ask board members a give a donation that is ameaningful gift for them. This allows the flexibility of having board members with various income levels the opportunity to serve on your board and support your organization.