The gifts we give to the church are not supposed to be comfortable, though we may grow into comfort with them. Our gifts become spiritual when there is an element of sacrifice present in our sharing with others, when we require ourselves to rearrange our finances to make room for our church pledge. Our gifts are not supposed to make us suffer either, however. Somewhere there is a balance. It is the job of church leadership to help the congregants find this balance in their lives.
Many denominations start with the tithe as the basic level of giving.
The tithe is expected, pledging starts after that. Half of a tithe does not seem an unreasonable target, even in UU churches. So, rather than fix a particular dollar amount as a minimum pledge, let's fix a minimum percentage. Anything less does not signify a serious commitment to our common future, and does not earn the rights of membership. Some contend that when we establish a requirement for monetary support before extending the right of voting membership, we invariably and unfairly discriminate against those less well off financially.